Xander Berkeley's "The Walking Dead" role has been revealed as Gregory, a character who -- in the comics -- was the leader of the Hilltop Colony and handed a few fan favorites over to Negan. TVLine points out that Gregory is "a coward to the core," poisons someone and gets on Paul "Jesus" Monroe's bad side, among other nefarious activities.
Berkeley was cast for "The Walking Dead" back in September, though at the time the character was nameless and only described as "relishing the superiority that comes with being in control, but he plays it off with a car salesman-type charm." Further, he was said to care just as much about self-preservation as Negan. This syncs up with the comic book character, in that he gives up Glenn and Maggie to Negan for his own self-preservation.
Additionally, Berkeley's Gregory is in the show for the long haul. Despite the fact he will debut during the second half of the season, his deal has a series-regular option for season seven.