I can only speculate as to what he was like before he started splicing, since his audio diaries in the game all seem to come after the discovery of ADAM. My personal headcanon is that he was a generally caring plastic surgeon, but a nitpicky perfectionist.

Via the audio diaries you can see how he descends into madness. He starts "seeing" and "speaking with" the goddess Aphrodite, who tells him that she can show him a new kind of beauty; that they need to do something about symmetry. By the time we see him in person in the game he's a nutball butchering people in an attempt to make them beautiful according to the skewed ideas of beauty "Aphrodite" has given him. (He has a machine gun under his operating table. >_>; ))