Doctor Ciel (シエル Shieru?) is a fictional character in the Mega Man Zero video game series. Although not a playable character, she is considered the female lead and heroine of the series, having important roles in most of her appearances.
Ciel is a human and former Reploid researcher that worked for Neo Arcadia. When Mega Man X disappeared eight years before the events of Mega Man Zero begins, Ciel created Copy X to replace him. Amazingly, Ciel is aged 14 during Mega Man Zero, which means she built Copy X at the age of 6, making her a child prodigy. According to the "Mega Man Zero Official Complete Works" source book, she is one of the genetically altered children born from Neo Arcadia experiments with DNA, which is what allowed her to attain such a high level of knowledge at such a young age. Additionally, one of her ancestors, another female scientist, was apparently directly responsible for the creation of the original Mother Elf, from which all other Cyber-elves were spawned.
However, when the Neo Arcadia government began oppressing and executing Reploids to solve their energy crisis, Ciel migrated with Reploid refugees to a ruined city when she was 9 years old. Knowing they were being falsely accused, and that the one behind it all was her own creation, she felt guilty and decided she could not stand by helplessly, and she soon became somewhat of a mother figure to many of the Reploid refugees, particularly a young girl she named Alouette. Times grew more desperate, though, and she eventually found her only hope to be uncovering a legendary hero that most people didn't even believe in anymore: the legendary Maverick Hunter Zero. She sought and eventually found him, though it took the sacrifice of one of her Cyber-elves, Passy, to wake him up.