He is David Robert Jones, an antagonist from Season 1. He worked with ZFT and The Pattern using the advanced science and technology that Walter and William Bell created to prepare "recruits" (people who had potential for super-human powers, including Olivia) Over Here for the coming war with Over There. In so doing, he broke numerous laws, was chased down by the Fringe Team, and in the end was killed by Peter cutting him in half by turning off the portal he was traversing (as mentioned in S4E8).
Note: All of the above were witnessed in the original (S1-S3) timeline Over Here, it's unknown what the history of the David Robert Jones shown at the end of Fringe S4E8 is, as we haven't seen that timeline. In addition, we don't know if this is "Over Here's" David Jones, or if it's "Over There's" David Jones.