How did Wesker from Resident Evil 5 become Evil and Why

Wesker started off as a researcher for the T-Virus, after he had escaped Racoon City when the T-Virus broke out, he realised how powerful the T-Virus was and how he could use the T-Virus experiment to help him succeed. He injected himslef with the T-Virus, oblivious to the effects it would have on him. In Resident Evil 5 he is the vice president of Umbrella Coorperations. He develops a new experiment called "Uroboros", the extraction of plant energy to be then mixed with a new formula, much more powerful than the T-Virus. He planned to use the Uroboros experiment to take over the African Continent then the world.

no wesker did not inject himself he was one of the wesker experimental children he was already strong to begin with but their was problems with the wesker children they needed to be injected every now and then but it was not the t-virus. William birkins was the one who kept him in check with his medicine hence the reason to why he did not die by the hands of tyrant in part 1 he was always going to be evil because he wanted to be known as a god