Gabe Lowen joined Beauty and the Beast as a beast who was hoping to use Vincent's blood to cure his own condition. When Vincent was kidnapped at the end of Season 1, Gabe was killed. Cat brought him back to life, and when he awoke the beast in him was dead.
In Season 2, Gabe has taken the role of police chief as a way to help Cat first track down Vincent and, once he was found, to find a way to cure Vincent as Cat cured him so that he could in some way repay Cat for all she had done for him.
Tess thinks that Gabe is harboring feelings for Cat beyond gratitude, so nobody knows how that will play out in the future.