Thomas Johnson Jr. was a Starfleet officer in the late 23rd and early 24th century. He served as commanding officer of the USS Enterprise-B from the early 2320s through the ship's loss (and presumed destruction) in 2329.
Johnson's first assignment as captain of the Enterprise-B was a patrol of the Cardassian border. The ship was therefore able to render assistance to Bajoran refugees in 2328 when Cardassia annexed Bajor. The following year the ship was lost in deep space shortly after the crew contracted some unknown infection. (USS Enterprise Owners' Workshop Manual)