Heimdall is one of the Norse Gods who appears in And Another Thing..., along with Thor. Loki and Odin were also mentioned. He guarded Bifrost, the Rainbow Bridge, and did not get along with Zaphod Beeblebrox, setting dragons on him.
He was also sometimes called Bentstick, a nickname given to him by Loki, which he hated. It was his name of power, so when Zaphod called him this, he was forced to obey.