Earlier on in his life, Zelgadiss had an desire to gain power. His great-grandfather, Rezo the Red Priest, came to him and offered a trade: in exchange for Zelgadiss' help in finding the Philosopher's Stone, Rezo would give him what he so desired by giving him the power he so desired. Zelgadiss jumped at the chance and that's when it happened -- Rezo had turned Zelgadiss into a chimera and he was, in addition to being one-third human, now also one-third golem and one-third brow demon.

Although his new form is indeed more powerful and resourceful, Zelgadiss hates it and has devoted his life to finding a way to restore his original body. He resents Rezo considerably for betraying his trust. Not happy with this new situation, Zelgadiss began to look for the Philosopher's Stone so that he may use it to return his body to normal. He eventually betrayed Rezo by helping Lina Inverse escape after kidnapping her and finding that she didn't have the Philosopher's Stone with her. Unfortunately, when they did get their hands on the Stone, Rezo swallowed it and it was destroyed as he transformed into Ruby Eye Shabranigdu. With the Stone gone and Rezo defeated, Zelgadiss was free to spend his time looking for a possible cure to his curse.

While Zelgadiss hates being a chimera, he does realize that it has certain benefits that his human body did not. His golem and brow demon traits do come in handy for a variety of situations:

Golem are creatures made from stone and are generally very sturdy. Because he is one-third golem, Zelgadiss' skin is as hard as rock and cannot be penetrated by weapons like axes and swords, or small amunition like arrows and bullets. It also makes him rather heavy; while he doesn't seem to break chairs when he sits on them, he's certainly heavy enough to be used as an anchor... ^^;;

His golem third also makes him considerably stronger. He's able to lift very heavy objects with ease. In Slayers TRY, he's the only one who is able to pick up Filia Ul Copt's mace, a weapon so heavy that only a golden ryuzoku can weild it!

Brow demons are a type of goblin and are not mazoku, like many seem to think. They aren't strong creatures but their capacity for magic is far greater than that of any human's. This gives Zelgadiss a cutting edge over other sorcerers, as he's able to use spells that they may not due to a lack of magical capacity. Brow demons are also very fast, so Zelgadiss can run at least three times as fast as any human.

Zelgadiss gets his blue skin and pointy ears from his being one-third brow demon. His senses are heightened and are more sensitive than that of a human's; he's demonstrated his excellent hearing on more than one occasion in the series.