W.M. Jefferies
- Full Name: W.M. Jefferies
- Species: Human
- Gender: Male
- By 2143: Captain, commanding officer, Earth Starfleet; NX Project (ENT: "First Flight")
- Still in that position by 2151 (ENT: "Home")
- By 2155: Captain, UESPA liaison, Starfleet Engineering, Earth Starfleet; Cochrane Institute, Alpha Centauri III (ENT Novel: Beneath the Raptor's Wing)
- By 2163: Commodore, Starfleet; Starfleet Corps of Engineers (ENT Novel: A Choice of Futures)