Eric, as we all know, did Dauntless initiation with Four (this is in Divergent) and Eric ended up with the leadership role after Four backed out of it.
Eric was in touch with Jeanine Mathews while a Dauntless and had plotted an attack against Abnegation. To do this, the Erudite had a serum that allowed for a simulated battle (just like the fear landscape).
After the battle, Eric was one of the few that didn't actually get the serum because he gave it out.
Where was he and where did he go after the invasion? I have no idea, I have read the first book and watched the first movie, but nothing suggests that he was still around.
Where did he go?