http://en.wikipedia.org/wiki/Solomon
Here's the Wiki on King Solomon, who was described in legends as being the master of demons and spirits, among other things. It might give you some ideas, and there's some really interesting/entertaining stuff here.
Also, as much as I'd like it to be different, I can't see any thematic reason for a diabolist/summoner to have the healing ability. It just doesn't obviously fit. Immortality, possibly, but it would require a good backstory, to make me believe it
