Sigma

* See also Minervas Den (DLC)
* See also Alphas
* See also Porter
* See also The Thinker
* See also Wahl
* See also Subject Delta
* See also Subject Omega ( Sinclair at end of BS2 )
* See also Handyman
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Sigma is the Player Character in the Minervas Den (BS2) DLC.
He is an "Alpha" early test model "Big Daddy" ( probably before that term was coined ). 
He is sent on a mission by Tenenbaum to retrieve materials to allow her to further her attempts to Cure Rapture's ADAM addiction ( presumably for the remaining people, which SHE was instrumental in causing ). To do so, Sigma must reach 'The Thinker', a powerful computer that allegedly runs much of Rapture. Of course, there are forces standing in Sigma's way.
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Sigma is an Alpha - Why is He Wandering Around ( Near Rapture Central Computing )?
Alphas are previously only seen around Fontaine Futuristics ( so there is something to be filled in there ).
Tenenbaum sent Sigma (Minerva Den) ? ( How did she get him ? ) Apparently she aimed him at The_Thinker. ( Wasn't Rapture Central Computing supposed to be 'cut off' from the rest of Rapture ? Little Details ... )
Subject Sigma was recalled to Minerva’s Den by The Thinker itself, You can (in-game) find the punch cards detailing the order in the 'Core' control room input console. 
Sigma is just blundering around just outside Minerva's Den when the DLC game starts ( without his 'Little Sister' ). Nothing previous is known by YOU (Sigma). Sigma is mute like Jack - no internal thought monologue and no replying to messages. "Awakened" ... Big Daddies needed routine maintenance, and perhaps Tenenbaum (or a confederate) slipped in to 'fix' him at some point. The ease that this seems to be achieved is getting repetitive, and there has to be 'more going on' than the Player gets to see ( The MMORPG will allow more elaboration to explain it all - Flashbacks ).
What explanation is there on how Sigma (an Alpha) wasn't bonded to a Little Sister ? Maybe his original LS got killed, and he fell into a coma or madness ? But possibly when Tenenbaum (or someone else) reactivated him and removed some of the mental conditioning - that bond/drive to have a Little Sister by his side was removed ? Perhaps at that point Sigma is just assigned to do maintenance.
It, is strange, because that other Alpha, Delta, seemed to possess even more 'Free Will'. Yet his powerful physiological and emotional bond to Eleanor was one of the aspects of his condition which both Eleanor and Tenenbaum were unable to remove, no matter what. We should get more of this explained.
For the case of Sigma and his original Little Sister 'pair bonding' : Not all Alpha Big Daddies died when their Little Sister is killed/saved/whatever. The reactions variedAudio Diary detailing this ?. Tenenbaum perhaps was responsible for removing/adjusting alot of such 'conditioning' as part of her other fixes to Sigma. 
A question might be : If she could do such things to any Big Daddy, why risk sending the ACTUAL Porter in to Minervas Den ??? Any other Big Daddy could have worked as well, no ? Nothing Porter specific (self-realization) seems to be done there. 
REALLY (again) it is because the gamewriters had to hide it from YOU (the Player) to not spoil their plot 'Twist'. Genetic lock broken ? Again, why not use any Big Daddy so to not risk this crucial Computer Expert, which Tenenbaum desperately needed to rebuild a Thinker type machine on The Surface.
!!! My Bio-Electronics technology could be required to build that computer up there too ( So the MMORPG REDO would have had Sigma make a stop at McClendon Electronics to get the Technology Process Information for that ).
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Did We Kill 'The Thinker' ?? :
As Sigma, did we kill off everyone who had continued maintaining The Thinker ? So is it now going to die ?
The technology "The Thinker" had been rebuilt with ( the vacuum tube stuff NEVER really worked out ) was alot more stable, and the system also has redundancy/flexibility built into it to bypass failing components ( a routine occurrence with those old time computers ).  Also, there were alot more people there in Minervas Den than we ever saw ( we never saw where they eat and sleep, etc ... ) - We saw only a small part of the entire place ( for it to exist in a mostly 'cutoff' state from the rest of Rapture. )  They (Minervians) would eventually creep out and continuing the only thing they had done for years - servicing the computers ( and mopping up the blood YOU spattered everywhere ). Even with Wahl gone, the routine would continue ( probably with advice from The Thinker itself  -- Interesting conversation : The next phone call from Hephaestus or Neptunes Bounty ).
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Psychology of The Thinker - "Well I'm not going anywhere fast, so might as well keep things running while I figure out what to do next."  News of Porter and Tenenbaum's failure on The Surface forced a 'rethink' ... (( Note the Thinkers Sentience may be greatly overrated, and it is really directives that Porter himself left imbedded in its programming. OR to really push in new 'Canon' we can have some 'Great Oz' (real person) type character who is really there causing it to happen - from 'Behind the Curtain' ...))
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