i think i read somewhere that the box cover of the guy that looks like baal is a character in a story that he made up, the prime evil's father... if i'm not mistaken
Quite correct. In the fictional Diablo III story kicking around in my head the metaphorical "Father" of the three brothers is the final boss in the game. He is, however, supposed to have most resemblance to Baal - his favourite "son".
PS: In response to your question, Asp, no. I am not in Blizzard. Although I would love to be.