Jack Casden was a 23rd century Human man who was a Starfleet officer. As of 2255, he was assigned to Starfleet Intelligence in San Francisco. While there, he befriended fellow Intelligence agent Gage Darres. After serving together for two years, they went on to different assignments, but were briefly reunited in 2263.
In 2264, Captain Casden was assigned as commanding officer of the USS Sphinx. As captain of the Sphinx, Casden transported a number of scientists to a secluded station in the Lantaru sector, under what he believed to be legitimate orders from Starfleet Intelligence. When he learned these orders were suspect, and he began to question the work being done by Dr. Bendes Kettaract. This led to the sabotage of his ship, and his murder by an unknown assailant, one likely connected with Section 31. (TOS - Section 31 novel: Cloak)