The Head was a powerful being from the higher dimensions.
It pursued Iris Wildthyme because it wanted her knowledge of the Multiverse. For several months, she hid from the being in a variety of realities. Eventually, she put her memories into a mind crystal from Marlion to protect them from the being. She then landed in Sherwood Forest and met up with Robin Hood and his merry men, who took Iris to the 2000s.
Iris eventually landed in the office of Satan & Satan, a publishing company and secret offshoot of MIAOW, where Tom and his sentient toy panda had been trying to convince Mida Slike to cancel the Iris Wildhtyme book series. The Head controlled everyone in the office and tried to make Tom give him the mind crystal, but Panda wasn't affected because he didn't have a brain and took the crystal from Tom. Under instruction from Iris, Panda shattered the crystal and Iris' memories were seemingly lost forever. With this, the Head left. (AUDIO: Wildthyme at Large)