Dr. Gillian Foster is Dr. Lightman’s professional colleague and close friend. Foster is the Lightman Group’s resident psychologist, and often acts as a counterbalance to Roth’s unconventional methods. Though they don’t always agree, Foster and Lightman work as a team and hold the understanding that they will keep their professional skills separate from their personal lives. The character is loosely based on Dr. Maureen O’Sullivan, a psychology professor who helped Dr. Paul Ekman (the inspiration for the series) with his research.

Kelli Williams is an American actress born in Los Angeles on June 8, 1970. Williams began her acting career at a young age, appearing in commercials since she was a baby. She is best known for her roles in The Practice, Lie to Me, and Army Wives. In 1996, Williams married author Ajay Sahgal, and together they have three children.