The New Faces of 'NCIS: Los Angeles' Revealed!

It's a new town, a new cast of characters, but it is still "NCIS," when CBS premieres "NCIS: Los Angeles," starring Chris O'Donnell and LL Cool J, this fall. So get your scorecard out, because ET has the lowdown on the spinoff direct from its creator Shane Brennan and the cast.

According to Brennan, the entire series was based around one character: Special Agent G. Callen.

"When I met Chris, I instantly knew he was Callen," Brennan tells ET. "I saw a photo of him with his head shaved and a little bit of growth. I said, 'That is the guy.'"