Captain Stillwell was a Starfleet officer in the 22nd century.
In 2161, after the decommissioning of the Enterprise NX-01, Stillwell offered Enterprise helmsman Travis Mayweather a position under his command. Preferring to remain under the command of Captain Archer, however, Mayweather refused to supply Stillwell with an immediate answer, instead deciding to wait to discover what position Archer intended to take. (ENT: "These Are the Voyages...")
Captain Stillwell was not seen on-screen, only referenced. He was named for production staff associate Eric A. Stillwell. There was a later Federation Starfleet officer named Eric Stillwell.