To cut the long story short, there are several common phrases/stereotypes that this guy represents:
1. The most obvious one, what a DOOM player might say at one point while playing the game, either frustration or happiness.
2. A criminal who is about to rape you/steal your whole house
3. A nearly dead soldier on the battlefield who starts to ask for unreasonable things or gets distracted like a complete idiot (i.e "My friend just got shot! Oh hey look, I found a penny!")
4. Any kind of weirdo who might look like the picture when he says something.
The bloody doom guy mostly portrays the main Doom character as a criminal with a sick sense of humor. The character is either frustrated, because he's about to get either killed or beaten, or the character is extremely happy and seems like he finally reached his goal. The character also sometimes represents the frustration many people get when playing challenging games.