Trigon
Trigon is an interdimensional demon of great power and the devil of the Teen Titans Justice League and DC universe. He is the ruler of the Underworld and his one desire is to take over all the worlds in the cosmos. To do this he chooses mortals through which he can use as gateways into their world and take it over. He has done so before by taking on a limited human form and mating with mortal women and baring a child. His bride and child are then used as his "gems" into the world through which he can unleash his full power. A young superhero by the name of Raven was his latest gem, but he would fittingly meet his end at her hands.
Trigon resurrects the Titans' foe Slade to force Raven into releasing him upon the Earth. In the three-part finale, "The End", Trigon finally emerges and destroys the Earth; the Titans are spared by a fraction of Raven's power, which she had given them before releasing Trigon. The Teen Titans, joined by Slade, launch an all-out assault on Trigon, but are ultimately too weak to defeat him. In the end, it is Raven who defeats him, using her own powers to obliterate Trigon, undoing the destruction he had caused in the process and the potential conquest of every world in the cosmos by his demonic followers.