The most defining characteristic of Hansel's personality is his hatred of witches. He considers killing witches his purpose in life and lets nothing get in the way of it. This is due to the trauma he experienced after his encounter with Frau Totenkinder.
Hansel lived with his sister Gretel and their father. When his father got remarried, his new wife forced him to leave his children in the woods to die. Frau Totenkinder, who lived in those woods, turned her house into candy to lure the children to her, so she could sacrifice them. The two were able to turn the tables and kill her. Hansel's obsession with killing witches began that day.
When the pair escaped the woods, the Adversary's armies were attacking the surrounding area. Hansel concluded that God was allowing demons to attack these people as punishment for their sins. The siblings kept ahead of the Adversary's armies, eventually coming to the mundane world, where they assumed all the good people were gathered.
Hansel and Gretel signed the Fabletown Compact and arrived in the Fabletown happy enough. When Hansel saw Frau Totenkinder, he became angry and left the settlement. He became a famed witch hunter in Europe.
He returned to America during the Salem witch trials. While there, he visited his sister in Fabletown. He was shocked to discover that his sister was studying witchcraft. Enraged, he struck her and broke her neck. Officially, the story was that she fell down some stairs. Hansel was never charged with murder, but he was struck from the Fabletown Compact and expulsed.
In Service of the Empire
As witch hunting became rarer in the mundane world, Hansel disappeared from the public eye. He returned to the Homelands. There, the Empire employed him as a witchhunter, seeking out anyone doing unauthorized magic.
More recently, Hansel was made an ambassador to Fabletown. Officially, his mission is to negotiate a treaty between them and the Empire. His true purpose is to rescue Baba Yaga and Geppetto's wooden soldiers.