Peter Killian Gallagher is an American actor. Since 1980, he has played roles in numerous Hollywood films. He is best known for starring as Sandy Cohen in the television drama series The O.C. from 2003 to 2007, recurring roles such as Deputy Chief William Dodds on Law & Order: Special Victims Unit, Stacey Koons on the Showtime comedy-drama Californication, Nick on the Netflix series Grace & Frankie, and Chuck Cedar in Mr. Deeds. He also played CIA Director of Clandestine Services (DCS) Arthur Campbell on Covert Affairs. He also is known for his roles in musical theatre, his most well known role being Sky Masterson in the 1992 Broadway revival of Guys and Dolls.

Sanford "Sandy" Cohen is a fictional character on the FOX series The O.C., portrayed by Peter Gallagher.