The Head was a powerful being from the higher dimensions who was literally a head on a stake.
It was one of the forces that pursued Iris Wildthyme for her memories after she stored her them in a Memory Crystal from the Mines of Marlion, entrusting it to Thomas Daley before leaving with Robin Hood and his Merry Men, who were secretly in the Head's employ. When Robin betrayed her in the Greenwood and brought her to the Head, it found that she did not have the crystal and took control of her, making her pilot the Celestial Omnibus to Tom at Satan & Satan Ltd.
There, the Head was almost successful in taking the Memory Crystal from Tom, but Panda, upon Iris' instruction, destroyed the Memory Crystal and the Head was dispelled back to the higher dimensions. (AUDIO: Wildthyme at Large)