Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
MULLIS
As described in historical dictionaries
Patronymica Britannica (1860)
MULLIS. Perhaps a corruption of Mullins, like Collis from Collins.
Origin: English
Region of origin: British Isles
Country of origin: England
Religion of origin: Christian
Language of origin: English