Caroline was a Human woman with whom Jonathan Archer had a relationship sometime prior to 2143. She ultimately left Archer and Earth when she moved to New Berlin. On the day Caroline left, Archer visited the 602 Club and began to drink heavily.
In 2143, when Archer again began to drink heavily at the 602 Club after he was passed over as pilot of the NX-Alpha, Ruby commented that she had not seen Archer drink as much since the day Caroline left for New Berlin. (ENT: "First Flight")