The T-103 was created using the date obtained from the T-002 during the mansion incident. They were a vast improvement on the T-002 due to the fact they could be mass produced, were very good at following orders/easily programmed and have incredible lethallity.

The research into this mass produced marketable tyrant was done by a small community of researchers on Sheena Island.

They were used to retrieve the G-Virus during the Raccoon City incident, and they have been the base for a few other lines such as Ivan, Nemesis T-type and the T-103 on Rockfort Island.

The only way to defeat a T-103 effectively is to somehow either destroy it's inhibitor jacket or do enough damage that it removes the jacket itself and transforms into the Super Tyrant. By that point you better hope you have an RPG to hand... or a tank.