Yagi Toshinori, popularly known as All Might, is the former user of the One For All Quirk. He was born Quirkless, however, he inherited the powers of One For All from Nana Shimura, his master.

What was All Might's original quirk?

Many theories state that All Might still has his original Quirk, i.e., transformation, which helps him maintain his muscular state a while longer.

Is DEKU actually Quirkless?

Deku, unfortunately, is informed by the doctor that he is Quirkless. As understood by the anime, Quirklessness is a recessive genetic trait. In a circumstance where one parent is Quirkless and one holds a Quirk, the child will be born with a Quirk due to the dominant trait.