Captain Erika Hernandez, portrayed by Ada Maris, was introduced in the
fourth season episode "Home".

Hernandez was the second Starfleet captain given command of a starship
in Earth's Warp 5 program, and was assigned to Columbia (NX-02), the
sister ship of Enterprise (NX-01).

"Home", which took place in 2154, established that some years earlier
Hernandez and Enterprise captain Jonathan Archer had been in a
relationship, which was briefly rekinded during a therapeutic holiday
Archer took following the Xindi mission. Their relationship apparently
ended because they realized that their jobs would get in the way of a
serious relationship, but they both remained on good terms afterwards.

Later, in the episode "Affliction", Hernandez accepted the transfer of
Enterprise chief engineer Charles Tucker, though she had to withstand
complaints from her engineering crew, including requests for
reassignment, due to Tucker's hard-driving manner of working.

In "Divergence", the Columbia was used in a risky maneuver that allowed
Tucker to perform an EVA to access a sabotaged Enterprise while both
ships were still travelling at high warp. She later allowed Tucker to
stay aboard Enterprise briefly in order to oversee repairs.

She has a similar name to that of the Empress of the Empire Galactika,
Erika Klein-Hernandez, in the short-lived DC comics series Ironwolf,
debuting in 1973.