Mary Marg Helgenberger (born November 16, 1958) is an American actress. She began her career in the early 1980s and first came to attention for playing the role of Siobhan Ryan on the daytime soap opera Ryan's Hope from 1982 to 1986. She is currently best known for her roles as Catherine Willows in the CBS drama (2000–12, 2013) and the subsequent TV movie Immortality (2015) and as K.C. Koloski in the ABC drama China Beach (1988–91), which earned her the 1990 Emmy Award for Outstanding Supporting Actress in a Drama Series.