Hodrick is a mad Hollow knight, a servant of the Mound Makers Covenant. It is possible to encounter him in a few locations throughout the game, as a Mound Maker PvP summon, or if you pursue Sirris questline, as a foe in her world.
Reaching Hodrick in your world alive is tricky, to say the least. He resides in the Pit of Hollows, beneath the Rotted Greatwood. However, if you kill that boss, the floor collapses during the battle, killing Hodrick.
The only way to meet Hodrick alive is to locate a Hollow Manservant wearing a cage on its back, just north of Item 12 on our Undead Settlement map. Approach it quietly from behind and you can press the use key on the cage to enter the cage and you will be deposited in the Pit of Hollows!