The Maxims were Huguenots (French protestants) who fled the persecution of Catholic King Louis XIV. Hiram's great-grandfather Samuel Maxim emigrated to Massachusetts sometime around 1710. The spellings of the surname bounced around a bit, some preferring Maxam, others Muxham, Moxom, and Maxham. I think roughly half of the modern descendants live in Vermont.
Hiram, his brother Hudson, and son Hiram Percy were prolific inventors, mostly in the field of armaments (sadly). Hiram was born in Maine but moved to England and was later knighted.
I am not a direct descendant but am in the (fairly sparse) family tree under Samuel.