Nathan Fillion is going to be returning to the Haloverse very soon, when Halo 5 launches. Reprising his role of Buck, Fillion looks like he is going to have a pretty significant presence in the game, especially where the story is concerned.
Appearing on Jimmy Kimmel Live, Fillion talked about getting scanned into the game, and jokingly saying he wants to be more handsome. With the press of a button (I'm sure this was exaggerated somewhat), it was so.
Take a look at the appearance right here.