Q: Okay. What'd you do?
A: I canonized him! Er. Canon'd? Look, the point is, the kid's a Tyrant.
Q: A what?
A: A canonical monster. The goal of the Tyrant project is to make an intelligent killing machine; a sort of. . . well, bearing in mind Resident Evil creatures are stronger, tougher, and faster than they should be, king zombie; not undead, although you do have to nearly-die/shut down under near-death conditions and reanimate to get there, and retaining its intelligence, which for most RE creatures is lost in the change. Birkin's version of the G-Virus made specifically for his bestest friend does that. And Deitmar got shot right through his tender little neck.
Q: Hold it, how'd he get this nifty virus?
A: Only Wesker can catch his virus. It's genetically modified just for him and locked down so it can't mutate and spread. But he could give it to himself if I were to have him destabilize his timeline being wishy-washy about whether or not he was going to change his own future--and thus the entire course of canon--and bring his older self into the bar.
Q: So. . . what?
A: Wesker got Wesker's room, stayed there overnight, and left a half-drunk glass of water when the older version departed. He's not usually that careless, but he was starting to get confused on whether or not he actually existed; and the younger version was simply too wiped out to think straight, much less remember he hadn't left a glass there. So now, yes. Sudden Tyrant.
Q: . . . uhoh.
A: No, not really. Deitmar should be watching people drift by like slow, soft, blood-filled targets, but. Hee.
Q: Hee?
A: Yep. See, instead of letting the virus run its course, he subdued it at every opportunity and did his best to fight it off. He wasn't physically an adult, either. So instead of reanimating him from "nearly dead" to "perfectly fine" in canon's span of roughly three minutes, it took about 6-8 hours and it barely got him back at all.
Q: So. . . what's with the violence?
A: Tyrants are sorta canon's king zombies. That drops them in the "monster" category. Deitmar is not human-only-niftier; he's a creature with an entirely new drive added on. Zombies crave food even when they're full; other varieties of Tyrants just desperately want to break stuff/blow stuff up/kill people/start fires. Wesker canonically craves power with something that's nearly desperation; I think part of that is the change. However, Ickle!Him nearly didn't get to Tyrant status at all and isn't nearly that sophisticated. He's got the garden-variety urge.
Q: New. . . drive? Urge? What?
A: Yep! Smashing stuff to itty bits sets off the reward centers in his brain, just like resting/drinking/eating/touching someone/other survival activities have little reward values of their own for the rest of us. He literally gets a high off violence, and it's a potent one; endorphins actually have a better effect than morphine, and he gets a flood of 'em. He hasn't figured out that killing things is better than smashing rocks, and killing with his bare hands is better than shooting something. I kinda hope he doesn't ever, actually.
Q: Drive suggests a need to fill it. So what happens if he doesn't?
A: Physiological suffering! Headaches, muscle cramps, confusion, incredible fraying of temper, and eventually memory loss and crowding out of other drives; his appetite will decline and he'll eventually forget to eat. As long as he smashes something about once every two days, he'll be fine.
Q: Temper frays? So wouldn't he break something and feel better that way?
A: Yep. Actually he thought for a while he was losing his humanity and becoming more distant each time he lost his temper. Nah. He's just plain not human anymore.
Q: So why'd you do this at all?
A: Canon demands a sacrifice! The core theme of Resident Evil is: "when evil strikes, you can fight or you can give in. Fighting means you'll probably lose someone important to you, but if you fight you'll get through." Canonically, main characters either constantly risk, or entirely lose, their loved ones. . . and occasionally have to shoot them in the head as Part II of that.
Wesker is the perfect villain of RE because in direct ideological contrast to the protagonists, he chose to work within the system to escape, not fight it, and later chose to adapt it to his ends rather than destroy it. Umbrella originally didn't tell him what he was into until he was hired and securely in the facility, and then presented him with a choice of being in the experiment or running it; and while he canonically planned future movement against Umbrella, he complied for the present to save himself and Birkin.
When Milliways and everyone in it gave him enough hope for change that he finally did take a stand, he naturally had to pay for it--remember, pretty much everyone in canon pays for their survival with a loved one. I wanted it to have serious consequences, so I went for the "death" route. I could have killed off the only person he cares about, Birkin. . . but loss of Birkin would kickstart his canonical isolated, sociopathic personality into taking over. Since two other pups belonging to two other muns would suffer deeply if that happened, plus he'd kinda be too psychologically iced over for anyone to want to play with, I chose to shoot him through the neck instead.
And doesn't he appreciate it.
Q: So why's he so. . . wonky?
A: Canon!Him can chuck people around like ragdolls, run in a blur, break heads on a whim, watch the world go by somewhere around four times slower for him than it does the rest of us, and shake off an entire craneful of steel beams falling on his noggin. Making him a Tyrant is inherently twinky. So I chose to make him pay for it by giving him a year of crazy klutziness.
EDIT: As of August 2008, he's not going to get the strength upgrade until he's an adult. Right now he's got speed and durability so he doesn't kill himself with it.