Dr. Karin Chakwas is a trauma surgeon and a major in the Alliance Navy. She served on the SSV Normandy under both Captain Anderson and Commander Shepard and was aboard the ship when it was destroyed by the Collectors. She later quit the Alliance in order to rejoin Shepard on the Cerberus-built Normandy SR-2. Along with most of the second Normandy's crew, Dr. Chakwas was kidnapped by the Collectors and taken beyond the Omega 4 relay, where Commander Shepard eventually rescued her.
After the Alliance impounded the Normandy SR-2, an inquiry found that Dr. Chakwas had "no significant role in or provable knowledge" of Cerberus's criminal activities. She has since rejoined the Alliance.