Tobin Dax
- Full Name: Tobin Dax
- Pre-Bonding Name: Tobin Fendus
- Species: Trill
- Second host of the Dax symbiont
- Gender: Male
- Son: Raifi Fendus
- Doctor of engineering, with focus in theoretical propulsion design (DS9: "The Siege")
- Interest in sleight-of-hand as a personal hobby (DS9 Short Story: "Dead Man's Hand"; ENT Novel: Tower of Babel)
- Vegetarian (DS9: "Afterimage")
- By 2154: Civilian advisor, theoretical engineering, UESPA
- Service included theoretical design work on NX-class, participation in Warp Seven Project, and Earth-Romulan War telecapture countermeasure development (ENT Novel: Beneath the Raptor's Wing, To Brave the Storm, A Choice of Futures; Destiny Novel: Gods of Night)
- 2161: Civilian advisor, theoretical engineering, Starfleet (ENT Novel: A Choice of Futures)
- Continuation of previous UESPA service
- 2163: Civilian advisor, chief engineer, Starfleet; USS Pioneer (ENT Novel: A Choice of Futures, Tower of Babel, Uncertain Logic)
- 2165: Resignation from Starfleet service (ENT Novel: Uncertain Logic)