As the daughter of filmmaker Donald P. Bellisario and actress Deborah Pratt, Troian Bellisario's entrance into the entertainment world was inevitable. Born on Oct. 28, 1985 in Los Angeles, Bellisario made her onscreen debut at the age of three opposite Tom Berenger and Daphne Zuniga in "Last Rites" (1988) - a film her father wrote, directed, and produced. The future star was often cast in minor roles on shows her father created, including the sci-fi series "Quantum Leap" (NBC, 1989-1993) and the military drama "JAG" (NBC, 1995-96; CBS, 1997-2005). Two of Bellisario's closest friends growing up were child stars-turned-entrepreneurs Mary-Kate and Ashley Olsen, who cast her in their 1998 film, "Billboard Dad," about twin sisters who attempt to set up their widowed father with a girlfriend by painting a giant advertisement situated above L.A.'s Sunset Boulevard. Bellisario also acted opposite her stepbrother Sean Murray on the crime drama series and "JAG" spin-off, "NCIS: Naval Criminal Investigative Service" (CBS, 2003- ). On the show she played the onscreen sister of Murray's character, a computer forensics specialist and a special agent for an elite team that investigates criminal activity in the U.S. Navy and Marine Corps.