Short answers, pulled from the story.
Gill was created by producer Tomoshi Sadamoto and designed by artist Akira Yasuda. The character was conceived as a religious leader with the ambition to control the world rather than a traditional villain.
Gill made his playable debut in Street Fighter V Champion Edition after appearing as an unlockable character in console versions of 2nd Impact and 3rd Strike. He was not playable in the original arcade versions of the Street Fighter III games.
Gill serves as the President of the Illuminati and seeks to create a utopia through the destruction of the current world order. He terms this plan the 2nd Impact and tests various warriors to coerce them into his cause.
Gill utilizes fire attacks on his right side and ice attacks on his left side based on his orientation. His body remains split perfectly down the middle with the right side burning red and the left side glowing blue regardless of which direction he faces.
Critics remain divided on whether Gill was a groundbreaking antagonist or a one-note character designed to showcase graphical power. Some reviewers mocked his backstory as ridiculous while others found him fascinating for his ability to resurrect himself and challenge player expectations.