* Mountain lion (Puma concolor): This is the most likely animal you're referring to. Mountain lions are at the top of the food chain in their ecosystems and have few natural predators. The only real threat to adult mountain lions are other mountain lions.
* Bobcat (Lynx rufus): Bobcats are smaller than mountain lions and can be preyed upon by coyotes, wolves, and bears, particularly when young or injured.
* Cougar (Puma concolor): This is the same animal as the mountain lion, so the predators are the same.
In short: There are very few predators of adult catamounts (mountain lions/cougars). The biggest threat to them is other mountain lions, especially during territorial disputes or when competing for resources. Young catamounts are more vulnerable to predation by coyotes, wolves, and bears.