
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 best known for her role as Catherine Willows in the CBS police procedural drama CSI: Crime Scene Investigation (2000–13) and the subsequent TV movie Immortality (2015). She reprised the role in the sequel CSI: Vegas (2022–present). Helgenberger is also known for playing the role of 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. She is also known for roles in the TV series Under the Dome and Intelligence, and the films Species (1995), Species II (1998), Erin Brockovich (2000), and Mr. Brooks (2007).
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Mr. Brooks
2007 · as Emma Brooks

Bad Boys
1995 · as Alison Sinclair

Erin Brockovich
2000 · as Donna Jensen

A Dog's Journey
2019 · as Hannah Montgomery

Species
1995 · as Dr. Laura Baker

Species II
1998 · as Dr. Laura Baker

Always
1989 · as Rachel

Fire Down Below
1997 · as Sarah Kellogg

In Good Company
2004 · as Ann

The Cowboy Way
1994 · as Margarette

Wonder Woman
2009 · as Hera (voice)

Almost Friends
2017 · as Samantha

Gold Coast
1997 · as Karen DiCilia

Just Looking
1995 · as Darlene Carpenter

After Midnight
1989 · as Alex (segment "All Night Operator")

CSI: Immortality
2015 · as Catherine Willows

My Fellow Americans
1996 · as Joanna (uncredited)

Inflammable
1995 · as Lt. (j.g.) Kay Dolan