Affleck, 30, is the younger brother of Ben Affleck; Phoenix, 28, is the younger sister of actors Joaquin and the late River Phoenix.
The couple first met through Joaquin Phoenix, Affleck's good friend since they costarred in 1995's To Die For. They became engaged in New York City over the 2003 Christmas holidays. Their son, Indiana August, was born May 31, 2004, in Amsterdam.
Affleck and Phoenix are both passionate about politics, animal rights and veganism. "He is a bleeding heart," Phoenix told Boston magazine of her then-fiancé. "He is the most generous guy I have ever met."
Phoenix has appeared on ER and in the HBO docudrama The Laramie Project, as well as in such films as 1998's The Faculty and SLC Punk!