A “secretive wizard” about whom little is known (FW). There is a bust of him in a Hogwarts corridor that Peeves has been known to drop on people’s heads (OP14). Harry received one of his Chocolate Frog trading cards during his first ride on the Hogwarts Express (PS6, CS/g).
Other canon notes and references
The bust of Paracelsus is probably the bust of the "ugly warlock" that was in the Room of Requirement when Harry hid the Half-Blood Prince potions book from Professor Snape in sixth year (HBP24). Harry threw the book into an old cupboard, and put the ugly bust on top, adorned by a wig and an old tiara. After talking to the ghost of Ravenclaw house, The Grey Lady, he realized that the tiara was actually the diadem of Ravenclaw, which Voldemort had turned into a Horcrux (DH31). Everything inside the room was later destroyed by Crabbe's Fiendfyre.
The wizard on Harry's Chocolate Frog Card is probably the same person as Theophrastus Philippus Aureolus Bombastus von Paracelsus , a "genius of alchemy" born in 1493. Born the son of a physician in Germany, he was exiled for his experiments on dead bodies (labeled "necromancy" in the Middle Ages). Afterward, he traveled extensively, all over Europe and eventually ended up in Constantinople (Turkey), where he learned some of the secrets of Arabian alchemy from sorcerers, witches and dervishes. He then went to Italy where he became an army field surgeon, using his "potions" skill to help heal soldiers, before making his way back to Germany where he became a professor of medicine and surgery. Although he made many miraculous cures, he was never very popular with other doctors, and was exiled again for his strong opinions and unorthodox cures, dying in Austria in 1541. (source: Wikipedia)