Mordenkainen The Planar Archmage

Mordenkainen was the first Archmage to perfect the creation of extra-dimensional spaces. He is known for making several spells along with several magical items. Some spells bare his name, some don't, but many believe spells such as Rope trick are his design. Bags of holding and Portable holes are also his making.
Mordenkainens known life spans 260 years. His legacy was cut short when he vanished in his own creation. Legend tells that Mordenkainen was trying to make spaces within spaces within spaces stacked upon itself, creating a maze-like structure only he could navigate. He vanished while inside his contraption.