Queen Sheba is the name of the entity tasked with the role of the ruler of Inferno. She is portrayed as a dark version of Jubileus, The Creator and is believed to serve the same role as it in her own realm.
In game description
"When the cosmos was split into light, darkness and the chaos in-between, the incredibly powerful Sheba was born alongside the darkness controlling the world of Inferno. She lives in the hellish land, and is often classified as a demon yet the full details of her existence are unknown." -The Book of Infernal Demons
Role in the games
In the first Bayonetta, Queen Sheba serve as the final climatic attack used against her light counterpart.