Jesse Eisenberg plays Zuckerberg who is portrayed in the film as a rather selfish, pompous, individual with quite a superiority complex. Eisenberg is an actor I will admit is not a favorite of mine, finding he gives a little too similar of performances in his various performances. Many of what he does seems frankly too calculated, and his whole style I really find he is just annoyingly self aware.
Luckily this works for this part quite well. Zuckerberg here really is an excessively calculating person, making everything he does has some sort of plan behind him. Everything that is, and Eisenberg's style fits perfectly for this calculated nature. One can see in Eisenberg the constant process that is going through Zuckerberg head at every moment never going away for a single second. It is interesting the way Eisenberg shows each plan for each moment, that are constantly swarming in his head. Whether it is his face book plan, or a small insulting remark, there is always the same calculation behind it. With this calculation though there is also a certain ease Eisenberg portrays in Zuckerberg making every move by Zuckerburg has this odd casual feeling to them them that is quite strangely effective.
Eisenberg has a perfect amount of icy determination in the role that fits the selfishness of Zuckerberg. Eisenberg manages to do this without overdoing it, even though it is another constant of his character, he shows it to be the nature of Zuckerberg, and it explains his abilities to do what he accomplishes in the story.This is perhaps a facade that he is trying to pull constantly though, in that he is always trying to act crueler than he is, meaner than he is, as well as smarter than he is. Eisenberg's constant forcefulness of his performance fits exceedingly well in suggesting the facade, making one properly wonder, is this guy completely for real?
The most important aspect of his performance though are his more subtle moments of his performance, where he shows that perhaps he is not nearly as cold as he tries to portray. They have a small but powerful moments by Eisenberg. They are usually done in small little reactions, that are spot on by Eisenberg, and add the right amount of depth to his character without overriding the rest of the portrayal. Eisenberg's performance here is an interesting work that really requires multiple viewing in order to be able to completely appreciate what he does in the role. It is an interesting performance because he has a consistent outward personality almost throughout, but Eisenberg very intelligently shows holes in his outward personality to great effect.