Howard was an employee of Plucky Pennywhistle's Magic Menagerie play store.
He used Tyler's drawings to physically construct fantasies into reality.
When he was a child, his brother drowned. He tried to tell his parents, but they didn't listen, so his brother drowned, and he spent the rest of his life blaming them for this. When he grew up, all he wanted to do was help children, that is why he got a job at Pluckies. He applied for manager, but was turned down.
Unable to help them that way, he turned to another method - harnassing the power of the childrens' fear. He brought their drawings of their worst fears into reality, and used them to kill parents who he thought were bad, causing a string of strange deaths.
He continued to work at Plucky's, while there using a super peppy attitude; he also managed to fool Sam and Dean, when Sam grilled him on him causing the death of another employee, who was going to tell Sam about him. He found Dean in the sub basement where he had created his rituals.
He also had sent two clowns to kill Sam. Dean confronted him on his guilt for his brother's death and used his magic against him by throwing one of his own pictures of his brother drowning into the fire. This caused his brother to come into reality, he then caused Howard to drown and with his death his magic was undone, and Sam survived.