Bill created the Pokemon Storage System. Because of this, he is blamed for the release of all the Pokemon throughout our journeies. His second in command is a Zigzagoon.
Working With Lord Dome
Many believe that Bill and Lord Dome are working together. This is because of an episode of the anime where Bill was in a Kabuto costume. Bill and Dome work together to destroy Helix and bring Democracy.
During FireRed, Bill was expirimenting on Pokemon, giving them weird new powers, and taking them to habbitats. Alice, the hero of FireRed, is thought to be Bill's daughter. She doesn't agree with what he and Dome are doing and sets out to stop him. Despite this, Bill loves and cares for his daughter.
In HeartGold, we learned that Abra was Bill's first Pokemon. His Abra later became a creature called Domalakazam.
Bill was killed at the second battle of Mt. Silver during War of the Gods. But his legacy lived on, Team Plasma in Black used his PC to try and release the Pokemon of others.