The Bog Roosh is the oldest underwater witch of all.
She was first seen in the story The Third Wish, were she said two her three granddaughters that she will grant them a wish if they pierce a spike in the head of her enemy (Hellboy). The three mairmaids capture Hellboy and take him to Bog Roosh. After she kills the two of her grandchildren, because of their wishes, she grants the third wish of the mermaid and tells her to leave. She describes to Hellboy her vision. His right hand taken ad himself dead. She also says that the Hand will be used to free the Dragon, the Ogdru Jahad.
Hellboy says that he has listened to all that before and tries to punch her. Bog Roosh drops him in hole in her cave where he remains nearly 20 months. When he wakes he finds himself in David Jones Locker, killing the sea cow (as pronounced by Grouagach) and freeing from his capture by the third mermaid who has now become the Bog Roosh. Hellboy says that they can leave now, but the little mermaid states that she cannot leave now that she is the new Bog Roosh. She frees Hellboy from the spike, and lets him leave in the ocean. As she was leaves the ghost of her father says that he will be with her even in the end of time.