Eko is the Yoruba name for the city of Lagos (which is in Lagos State, the old Capital of Nigeria). His name is a symbol of the city. In Yoruba, Eko is symbolic of home, thus his name, Mr. Eko, resonates only with Nigerians who understand its true meaning.
Adapts to life as a priest when he stays in disguise.
Eko was killed by the Monster because he failed to atone for or admit to his past sins.
Or it could be the opposite, Eko finally atoned for his sins and was ready to die.
Well, he didn't exactly atone, he said he's got nothing to be sorry for and that he had not sinned, but rather survived.
Eko was most likely scanned, as Ben was in 'Dead is Dead' and then judged, like Ben was in that same episode. Unlike Ben, Eko refused to admit fault and take responsibility for his sins. So, having judged Eko guilty the Monster killed him. The Man in Black later states his belief that all humans are sinful and corruptible. Eko's refusal to admit himself as such could have caused the Monster to kill him for what he viewed as spiritual dishonesty. The Smoke Monster is later depicted with the Egyptian god Infu (Anubis). After death, the Egyptians believed that your heart would be weighed by its sins against the feather of truth by Infu, and to save yourself from destruction, you had only to be 'true of voice', to admit to the sins your heart had committed. If you came clean, you would be judged worthy. If you did not, then your heart would be fed to the monster Ammit. Perhaps a similar process was at work in Eko's death.
Eko was judged and killed by the monster because he did not seek redemption anymore and thus became useless to Smokey, who needed people to be corruptable to further his goals. Up to that point Smokey was planning to use Eko in a similar way as he used Desmond at the source in "The End".
The first time Eko encountered the Smoke Monster, he stood his ground. The second time, after being "judged," he doubts himself and turns to run away. Perhaps the Monster needs someone confident whom he can use, or perhaps Eko really was able to stand him down.
Now we know Smokey is The Man in Black, a more interesting theory appears: At the moment, Eko was replacing John Locke as the "man of faith" and was the one who wanted to keep pushing the button on the Swan. Probably, MiB was considering him as Locke's replacement in his plans to kill Jacob, however when tested a last time, he found him unusable and disposed of him, perhaps because his strong and unwavering resolve and confidence, as opposed to Locke's pathetic defeatism and self-pity.
The Man in Black may be kept on the island because of its electromagnetic properties. He needed somebody to stop pushing the button, hence he created the events that led Locke to the Pearl station, shattering Locke's belief in the necessity to push the button. Eko on the other hand continued to belief it was necessary to keep pushing the button. When Eko additionally quoted the 23rd Psalm, the Man in Black (as the smoke monster) realized that Mr. Eko would always be in (unaware) allegiance with Jacob. Thus he had became potentially dangerous to the plans of MiB and was killed.
The Man in Black, bound by the Rules, could not kill Eko because he was a Candidate. However, by refusing to atone for his sins, Eko failed his candidacy, and was able to be killed.
Eko was building a church at the time he was killed by the Monster
Eko atoned for his past sins, and the Island 'let him go'.
The writers have said that Eko will reappear, but not necessarily in a flashback episode.
People have seen 'ghosts' on the Island before. Jack saw his father and Eko saw his brother and Ana Lucia. Ben saw his mother. Therefore, the Monster will return in the form of Eko.
"Yemi" set his tent alight in order to get him moving, to "kick start" him, so that he would venture out in to the jungle and find the Monster.
The implosion of the hatch sent Eko back in time to the day of Yemi's death, giving him the chance to save his brother. Therefore in The Cost of Living the body could not be found, because Eko had changed the course of time and Yemi was never on the island.
The implosion of the hatch sent Eko to one of the "exit points" on the Island, like it did with Desmond. Similar what happened to Jack and the original Man in Black after they fiddled around with the cork at the source.
Eko tells Locke a story about The Book of Laws before revealing the hidden orientation footage. The story was about a king who built/rebuilt the temple with the book of laws. The book is also one of the items Richard presents to young Locke, supposedly the correct one Locke did not choose. Perhaps the unknown temple on the Island will be built/rebuilt by Locke.
The Monster judged Eko the same way it judged Ben, but found him "guilty" rather than "innocent", so it killed him.
Eko was killed by the Monster because, by letting go of his sins, was of no use to the Monster (as opposed to Ben, who was consumed by guilt during his "judgment", and thus could be easily manipulated)
Much like with Zoe, the MiB immediately killed Eko once it was clear that he was not going to be persuaded away from his own convictions.
Mr. Eko was originally intended to be the Yin to John Locke's Yan - his opposite in every way. The black to his white, the tail section to his fuselage, the Jacob to his Smoke Monster, and the good to his bad. In podcasts during Season 2, Damon and Carlton strongly emphasize Eko's relationship to Locke, how the two have a very mystical nature and how they will take their different paths. A rivalry is seen to exist in many instances during their mutual time spent on the Island. For example, their Swan adventures in the Season 2 finale. When it was learned AAA would be leaving the show, it was made sure that the character's departure would be mythologically significant in showing how The Monster did NOT take kindly to him. His last words were likely either: "I saw the Devil" as can reportedly be heard faintly, which alludes to the Monster's evil; "You're next" as inferred by the audience, which would predict John's future connection to the Monster; or "You're all next" as may also be inferred, which may imply that judgment by the Monster would be coming.
The Smoke Monster killed Ecko because he was a loop keeper as he wanted to keep the Swan in place.
Eko's death is a microcosm foreboding the end of the series. Eko had reached a point where he no longer felt guilty about his brother's death, he had 'moved on' in a sense. His recognition of the Smoke Monster's manifestation of Yemi as not actually being his brother, may have been the cause of the MIB's decision to murder him. It is safe to speculate that Eko is not in the final scene in the church in The End, is because he had moved on. In the episode a woman says to Eko, that he must build a church to make up for the one he lost after Yemi's death, explaining his motive to want to build one on the island (which lacked completion). His moving on, and the image of the unfinished church lay to the point that he had 'moved on' from trying to fix problems in his life. This image of young Eko and Yemi walking away, is analogous to the final image of the show, finally entering heaven (or nirvana, or eternity) with someone he loved, who was his brother. They met each other in a place the made for each other in their childhood. This is rough speculation, but it makes sense.
That they meet in a chuch in The End could be significant. If Eko owed Yemi a church, in a sense he could have built the church all the Losties meet in, in the afterlife. Eko was building a church on the Island, presumably to bring people together as well as pay his debt. The chuch in the afterlife could have been Eko fulfilling his debt further explaining why he wasn't there. His role was to provide the place of gathering for the others.
Looking into the Monster
When Eko looked into the Monster he saw answers to some of the mysteries of the Island. (e.g. lift up your eyes and look north). This is why the Monster killed him because it gave him too much information.
The Monster's "face" which faces Eko during his first encounter with it is a bearded man which is Jacob (disproven).
If the Monster is of religious nature, it disliked the competition Eko initiated by building a christian church.
The MIB wanted to use Eko to kill the candidates but he realized he couldn't use him anymore so he killed him.
When Eko died and whispered his final words to Locke, he announced them as "we're next." As confirmed in the November 6th podcast, Eko's final words to Locke were "you're next." This provides some ambiguity, though: Eko, in saying, "you're next," may have just been referring to Locke. If Eko meant "you all are next," Locke's interpretation would be correct - it refers to the Losties as a whole, or the group who went on the expedition to the Pearl.
Locke has misinterpreted a message before, Christian told Locke HE had to move the island, Locke told Ben 'WE have to move the island'. The same thing could have happened here; Eko says 'You're next', Locke tells everyone that 'We're next'.This also hints into the coming speech ben makes by saying that Locke's last words were I don't understand,which sort makes sense considering MIB/monster John talks about dead John as being a man who has always been since being on the island confused and LOST. Whereas MIB/monster has knowns many things about the island and has "found"its true meaning and purpose.
It is possible, as Hurley suggested, that his last words were referring to Nikki and Paulo who were the next people to die on the Island.
It was also confirmed Nikki was bitten by a creation of the smoke monster rather than real spiders. if you watch the clip you can clearly hear the monster around her as she looks around, then the spiders appear. so this would tie in with the monster/Eko's warning of who's next.
From the way he said it, it looked like the words were meant for John and John alone, so I doubt it had anything to do with the other losties.
He could refer to Locke as the next leader of the Others, the next guy who would be Jacob's spokesman, and that was who "the Monster said to Mr. Eko before killing him.
Further to this point, Eko could have been the Monster's first choice to do his bidding by overthrowing Ben, and when Eko "didn't work out" so to speak, he made his comment to alert John that he was the Monster's second choice for the job.
I have a feeling that Eko, as a man of faith himself, was in consideration, but in the end the Monster didn't like the idea. I don't know if Locke was a second choice, considering how much effort the Monster had put in through time.
His last words may refer to the Monster's next victim, a.k.a. Nikki she was bitten by the Monster's manifestation of a medusa spider.
Eko realized that the Island would never forgive him of his past crimes and he knew the Island would never stop until he was dead. So when he said, "You're next" to John he was saying that Island would focus on him now.
It could be that the entity (or person) that showed himself to Eko in the form of Yemi was Jacob's nemesis trying to gain influence over Eko. Its failure led to the death of Eko and the entity instead turned towards John. We know now that Jacob's nemesis needed a loophole in order to kill Jacob and perhaps the last words, 'You're Next,' uttered by Eko to John meant that the nemesis began focusing his plan upon John.
The Spiders are not manifestations, but rather part of the Monster itself, which would support this theory further.
Eko was referring to John's replacement of Ben as the Island's caretaker.
"You're next" was not Eko's last words. Locke lied about what he said for a yet to be revealed purpose.
Eko was telling John that he would be next to be judged by the island. He soon faces his biggest fear, his father, as Eko faced his sinful past.
Eko actually mouthed, "I saw the devil." This would coincide with John's earlier question of, "What did you see back there?...I saw a beautiful light." Eko responded by saying, "I saw the devil." The writers eventually changed it to make it more dramatic.
Perhaps Eko knew, as a result of an encounter of the monster which flashed images to him, of MiB's plan to have John killed so he can duplicate him. "You're next" refers to John in this context.
Because he was attacked by Smokey (a.k.a. Jacob's Nemesis), he may be working for Jacob.
Failed his recruitment initiation
We must all remember that the man in black/smoke monster does not play games and at this point he still needed to kill Jacob, looking at the survivors as an observer and as someone who can read people's past deeds, Eko would be the perfect candidate for killing Jacob due to his large size and the moral grey area he inhabits. The Monster, however needed someone pure of soul to kill Jacob, someone who was sorry for the crimes they have committed (Ben was sorry that he killed Locke). Eko, however, did not repent, and therefore became useless to the Monster who cast him aside as a failed potential candidate to kill Jacob for him... But, of course, Locke was the next element to the Monster's plan, hence 'you're next.'
What he died for
Perhaps Eko was a candidate (his name was never shown on the cave wall or in the Lighthouse, so this theory is a stretch). Jacob's candidates were all broken, unhappy people with a lot of problems to work out. Sometimes these people figure things out, or have other life opportunities come to them, and so are crossed off, I.E. Kate. The first time Eko meets the Smoke Monster, he is still troubled by his past life, searching for forgiveness, and so is still a candidate, thus the Man in Black can not kill him. When Eko forgives himself for his past life and moves on, his name is "crossed off," whether literally or figuratively, and thus MiB is able to kill him, easily.
This seems likely. Since we don't know for sure what his last name is, it's quite possible he's one of the names we've already seen. (If his name is Tunde, it's quite possible he's one of the names we haven't seen.)
Eko was not a candidate
If Eko is his first name, then the Eko referenced on the wall cannot be him. Only surnames are written on the wall means this other Eko was someone else. This also explains why the monster did not kill Eko straight away. Because Eko was always referred to as "Mr. Eko" the monster at first assumed he was the Eko on the last. Only later after testing did the monster realise that Eko was not a candidate and could therefore kill him.
If Eko is his last name this still does not make him a candidate. The reference to Tunde could in fact be his first name. If Eko is the surname, then there are two Eko's in Lost, the other being Yemi. Yemi was the candidate but was shot off Island. The Island sensing Yemi's death placed itself closer to the plane in an attempt to save him. This would explain how Yemi's plane came to crash on the Island. Mr. Eko's presence is a coincidence. Again if this scenario is the case then the monster was not sure which Eko was the candidate and therefore tested Mr. Eko to discover that he wasn't the candidate.
Either scenario also proves the theory that the list in the caves was MiB's. Lacking the mirrors he could not accurately identify which person the name indicated. He would therefore test anyone with that name to determine if they were a candidate or not.
Both brothers were candidates, but Eko's name is written in the caves. Eko was written on the lighthouse dial.