Contraction formed from the words 'he is the man'.
Originally derived from a mural (graffiti) painted (in the late 70's) on a wall in Australia . The mural depicted the face of a young Jesus like character and the words 'he de mann'.
It has been argued that the words underneath the mural do not refer to Jesus but to the name of the actual artist; hence, the funny spelling of the words.
Furthermore, it has been argued that the actual picture is not a Jesus representation but a self portrait.
Currently the word hedeman (or hedemann) it is not used in a Christian context but to indicate that a particular person is exceptionally good in a particular field, sport, etc.
There has been instances in which the first four letters of the word have been used to denote the excellence of something or someone (regardless the person's sex); for example, hedecar, hedeboy, hededog, hedegirl, etc.