Thomas LeBlanc was originally a human rapist and serial killer, until he was recruited for the Mutt uprising and was turned into a werewolf.
LeBlanc was a man-killer, or, in his case, a woman-killer. He enjoyed the hunt or torturing, raping, then slaughtering women, a group he chose as he no doubt believed they were inferior to him.
Once bitten and trained by Daniel Santos, an experienced and former Pack werewolf, he targeted Elena Michaels after she had snapped his wrist during a scenario in the Bear Valley Police Dept. whereupon Karl Marsten told the others in their group and had a good laugh at him. LeBlanc swore revenge against her, and tried to shoot her in an airport parking lot, where a woman he mistook for Elena was shot in the forehead by him.
When Elena surrenders herself to Daniel Santos in exchange for Clay's freedom, LeBlanc, not wanting the killing to end, swiftly slices Daniel's throat, leaving him to choke on his own blood. However, before he can try and kill Elena, the rest of the Pack arrive, forcing him to run but Elena manages to hunt him down and tear out his throat.
LeBlanc was an infamous rapist, serial killer, and a consummate misogynist, beholding a seething hatred of women. He kept a scrapbook of his exploits, with details, newspaper clippings, sometimes even trophies that reminded him of each woman he raped and killed.
After joining the Mutts and becoming a werewolf, he would hear of Elena Michaels, but his woman-hating nature caused him to underestimate her and mock her when they first met that Elena put him in his place by breaking his wrist. This caused LeBlanc's hatred to peak as he sought out Elena and attempted to kill her with a gun (even killing a blonde woman whom he mistook for Elena), despite the orders that Elena was supposed to be captured, not killed.
He didn't care about such orders because of his hatred and need to prove himself superior over Elena (and women in general).