Bergdahl was a human male and Federation Starfleet officer in the 23rd century. In 2268 Bergdahl held the rank of Lieutenant and served on the USS Enterprise as a lab chief. Noted for his similarities in appearance to Captain Kirk, Bergdahl was fairly close in age to Kirk.
Bergdahl had a reputation for being fussy and difficult to work with. Some members of the crew took to calling him Birddog. Spock found that Bergdahl reminded him of the two century old house steward that had made his childhood a burden. At one point Kirk noted in his personal log that an unusual number of crew members who had worked for Bergdahl had requested transfer. Ensign Emiko Adams in fact took a reduction in rank in order to transfer out of Bergdahl's department. (TOS novel: Ghost-Walker)