In Greek mythology, Pegasus is a winged horse, son of Poseidon and Medusa (a monstrous female on whom when gazed upon would turn onlookers into stone). Pegasus is associated originally for carrying thunderbolts for Zeus. He is generally pictured in white, sometimes in golden wings. The Pegasus was a great flyer.
There are two condition given for Pegasus's birth -
Pegasus was not immortal. Because of his faithful service, Zeus honored him with a constellation. On the last day of his life, Zeus transformed Pegasus into a constellation.
Pegasus and Unicorn