In the 5E release of Tales from the Yawning Portal there is the Module White Plume Mountain.
On page 95 it states the previous lore of Keraptis the Wizard:
Thirteen hundred years ago, the wizard Keraptis was searching for a suitable haven where he could indulge his eccentricities without fear of interference. He visited White Plume Mountain, going closer than most dared to and discovered the system of old lava-tubes that riddle the cone and the underlying strata. With a little alteration, he thought, these would be perfect for his purposes. The area already had a bad reputation, and he could think of a few ways to make it worse. So he disappeared below White Plume Mountain and vanished from the knowledge of the surface world.
Is there any more offical Lore from Wizards of the Coast, or Module writers or approved Authors on Keraptis the Wizard, or is this all there is?