Eko was MIB's back-up plan. (recruits, ghosts, etc) by Hayzeus

Back in Season 4, when we were unaware of MIB's existence (or were still very much in the dark, anyway), I posted a theory that in case things didn't work out with Locke, Jacob was planning on using Eko as a pawn instead.

Putting it midly, a few new things have come to light since them, but these new developments have also made parts of my theory stronger, so here we go:

MIB/The Monster seems to like manipulating people who've been through personal trauma. Sayid losing Nadia, Sawyer losing Juliet, Claire losing Aaron, Ben losing Alex, pretty much Locke's entire life. Another one we've saw him toy with earlier on was Eko. Locke was a perfect pawn for MIB: easily lead, gullible, desperate for acceptance, but also competent enough to carry on missions and of curse, Locke had a certain mystique about him and a connection with the Island- when he spoke, people generally listened.

If Jacob has candidates, then MIB has 'recruits'. Locke was the first character to survive a face-to-face meeting with him. MIB scanned Locke was dedicated to the Island and something of a spiritual leader amongst the Losties, and he had plenty of flaws to exploit.

But, of course, in Season Two Locke, after weeks of button-pushing, was losing faith in the Island. Less credulous, less pliable. MIB was in danger of losing the most important piece in his plan (save for Ben). Then Eko appeared.

Yemi's body had been on the Island for years, and when Eko himself showed up, MIB was able to assume his form more convincingly than any other. He had assumed Christian’s form, but Jack didn't even listen to his Dad when he was alive- no dice there. He assumed Dave's form to try and kill off Hurley (a known candidate for Jacob and able to speak to the dead)- with no luck, and he could only take Dave's form because Dave only existed in Hurley's mind. He couldn't even take the form of a person from Kate's past- he became a horse. He took Walt's form twice- once to get Shannon (another candidate) killed and once to motivate Locke out of the Dharma-pit (but even then Walt was taller, older, not a totally convincing illusion). And on top of that, the only person from Locke's past who he might have listened to was Helen- and even that mightn't have worked.

Eko however, felt tremendous guilt over Yemi- and MIB could take his form perfectly: which to MIB's mind made him probably even easier to manipulate than Locke. Locke and EKo were both also suited to jungle-life, men-of-faith, both involved in the drugs market during their life and both had key scenes with Ben (the other important pawn) in the hatch: Ben was afraid of both of them: Locke for his connection to the Island, and Eko by his sheer physical presence.

So MIB scanned Eko in his 'monster form'- and actually backed-down from a direct stare-out. Eventually, through Season 2, Eko became for devoted to the Island and Locke lost his faith. To MIB, they were both potentially useful pawns. However, after the Hatch Implosion, Eko was in danger from the polar bears and Locke wanted to renew his faith in the Island. SO the MIB took Boone's form: again, to manipulate Locke's guilt, and gave him 'further instructions' to save Eko's life.

Eko was the only person the MIB had any interest in keeping alive- for his final judgement. Locke was now more dedicated to the Island than ever, but MIB, who considered Locke 'irreparably broken', decided to test Eko first.

Crunch time: MIB took Yemi's form and wanted Eko to 'confess'- MIB wanted to finally psychologically break Eko through his guilt, in order to use him to eventually join the Others and use his form to get access to Jacob. However, Eko refused to confess, refused to apologize for the life he had lived, and so MIB shed Yemi's form ('you speak to me as if I were your brother)
and killed him. This wasn't about morality, it was because MIB had lost the psychological leverage he had with Eko, who was too strong to be broken by guilt. Rather than have him as a wild card and potential foe- Eko was most likely a candidate too, MIB decided to kill him and move onto his new pawn- Locke.

So there you have it. Who knows, if Eko had caved-in, he may have become the form Eko took to find Jacob, or he may heave become Locke's sidekick, muscle, or a herald for MIB in some other way. Theorise away, lads and lasses.