The captain of the Columbia, Earth's second Warp 5 starship, and a former romantic partner of Jonathan Archer.
Erika Hernandez was a Starfleet captain who took command of Columbia, the NX-class sister ship of Enterprise and the second vessel of Earth's Warp 5 programme. She and Jonathan Archer had a romantic relationship years earlier that ended because their careers pulled them apart, though they remained friends and respected colleagues.
When Archer returned to Earth after the Xindi mission, the two briefly rekindled their relationship while he recovered from the ordeal. Hernandez then departed on Columbia's first mission, and Trip Tucker transferred to her ship for a time before returning to Enterprise.
Columbia later worked alongside Enterprise during the crisis caused by the Klingon Augment virus, helping to rescue the ship and its crew from Klingon forces. Hernandez showed Starfleet's growing roster of capable commanders in the years leading to the founding of the Federation, and she remains a notable link in the history of the NX programme.