In Roman and Greek mythology, Priapus was a fertility god, protector of livestock, fruit plants, gardens and male genitalia. He was a son of Dionysus and Aphrodite. Sculptures of Priapus with large, ithyphallic genitalia were placed on gardens and fields to guarantee an abundant crop. He was much more popular in Roman mythology than in Greek.
He tried to rape Lotis, and she was changed into a lotus plant to protect her.
The medical condition priapism gets its name from Priapus.