Delcara was a female biped obsessed with the destruction of the Borg.
Delcara was a member of a warlike race called the Shgin. Her people were decimated by the Borg centuries ago. A powerful telepath, she came to live with the El-Aurians and was the bond-sister of Guinan, taking another El-Aurian as a mate. When the El-Aurians were also destroyed by the Borg, Delcara departed seeking a means to avenge her loss, her abilities eventually leading her to Earth, due to her awareness of a strange connection to then-Cadet Jean-Luc Picard. While telepathically visiting Starfleet Academy, she overheard Picard speculating about the Planet Killer's origins- Picard noting that the original Planet Killer could not have come from too far outside the galaxy due to the inability for the object to find fuel in the inter-galactic void-, leaving her resolved to find one and use against the Borg.
Delcara tracked the Planet Killers and commandeered one that was much larger and faster than the original. She used it to attack the Borg several times.
However, although Delcara succeeded in her goal of finding a Planet Killer, despite her essential intentions of destroying the Borg, her vendetta blinded her to the fact that she was no better than them, disregarding any inhabited planets her ship consumed as it travelled as necessary sacrifices to destroy the Borg themselves. She eventually became trapped in an infinite time loop when she accelerated to Warp Ten in an effort to reach the Delta Quadrant. (TNG novel: Vendetta)