Egbert the Egregious was a medieval wizard who was a one-time possessor of the Elder Wand. He killed Emeric the Evil in a duel to gain its possession (DH21, TBB).
In his writings on The Tale of the Three Brothers, Dumbledore notes that "what became of Egbert is unknown, although the life expectancy of medieval duellers was generally short" (TBB).
Egbert = "bright edge" from the Old English elements ecg "edge of a sword" and beorht "bright".
Egregious = conspicuously and outrageously bad or reprehensible.