The villain of Mass Effect 4 is the man shown in the N7 armor in the various trailers.
He is, in reality, Armistan Banes, an unexplored side character in the first Mass Effect game.
He's essentially going full warlord/Caesar to try and control the new colonies. He's not actually the father of the Ryders, although they believe he is, and he is not called Banes for most of the game.
Screencap this.
In the following video, at 1:58, you can see this N7 figure, with a Krogan sidekick, holding the Male Ryder upside down over a ledge, like Suge Knight did to Vanilla Ice.
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You can pause the video yourself to see this man's face and compare it to pic related, who is the male Ryder.
it has been suggested that this man in the N7 armor is the father of the Ryders, but he clearly has a deeply antagonistic relationship with them at best. He has his own trailer, which you can see here:
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How do we know this is Armistan? For one, he was an Alliance Black Ops man, likely earning an N7 designation. The only person in Mass Effect lore to wear this designation without earning it was Conrad Verner. Armistan also favors Krogan muscle and operates in a clandestine matter, going so far as to fake his own death. Is it unbelievable to surmise this man got aboard "The Ark" before it left for Andromeda? FemSheps narration in the following trailer shows that "The Ark" leaves either during or just after the Reaper War. You can see that here:
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Armistan is not an "agent of Cerberus", (although he once was, supposedly) he just has a god complex and sees incredible opportunity in Andromeda, and so he takes matters into his own hands. He is meant to be a nod to hardcore fans but otherwise is a blank slate for a story about a power hungry despot who destroys whole alien colonies in service of his goals.
