A Hookman is a creature of urban legend. The hookman story has been told many times and there are many different versions as well. He is summoned by someone to take revenge on those the person thinks deserve it. This creature appears its own self title episode in Supernatural. Although, he was not purposely summoned.
In Supernatural, the spirit was a man named Jacob Karns, a preacher in 1862, who was so angry about the red-light district that he went there one night and killed 13 prostitutes with a hook. Jacob was later sentenced to death and was hanged. His body was buried in an unmarked grave, and his silver hook donated to the church, where it was melted down and created into something else. Following that, the spirit of the hookman latched onto priests and their daughters.
Essentially, the hookman is a Violent Spirit. So it has the ability to appear anywhere, anytime. He has also shown that he can become invisible, can move through walls, and has enhanced strength. This spirit wields a hook as its main weapon. So hookman can cause physical harm. When the hookman is coming, he often drags his hook against things which his victim can see and hear. There is also a classic saying connected to him, "Aren't You Glad You Didn't Turn The Lights On?"
- Salt - Since he is a spirit, salt can be used to slow him down. Rock salt fired out of shotguns can also slow the Hookman down.
- Remains - Spirits can only be killed by their remains. Only thing left of him was the silver hook which was melted down into a cross.