Dashiell Kim is an astrophysicist who was abducted for a week, had a psychotic break, murdered his wife, and was institutionalized at St. Claire's Hospital. He and Walter Bishop became acquainted in the hospital.
Walter returns to St. Claire's to interview Kim for the Ben Stockton kidnapping case. From what Walter gathers, it is likely that Kim had been abducted by Joanne Ostler; his reference to a "red castle" where he was held leads Olivia Dunham to Ostler's location. ("The Equation")