After King Sisyphus of Corinth was condemned to the Underworld for trying to cheat death, his son, Glaucus, became king, and married a beautiful princess named Eurynome. Unfortunately, the gods were still angry with Sisyphus, and Zeus decreed that the royal line of Corinth would never have sons. Hence, Queen Eurynome approached Poseidon for help, and through him, she mothered a son, Hipponous.
Unfortunately, as Hipponous matured, he developed a reputation for recklessness and causing dangerous accidents. After he accidentally killed a man named Belleros, he came to be known as Bellerophon, which meant "the killer of Belleros". Later on, he accidentally killed his own brother, and his parents decided to send him to a neighbouring kingdom, Argos, to atone for it.
During his journey, he encountered a roadside shrine to Athena, and tearfully prayed to the goddess for guidance before falling asleep. Despite the rivalry between her and Poseidon, the goddess pitied him and recognised his hidden potential to be a great hero. Hence, she appeared to him in a dream, explained his true heritage to him, and gave him a magical bridle to catch Pegasus, the legendary immortal winged horse. Due to the magical bridle and Pegasus' surprising compliance, Bellerophon successfully gained a flying horse that would take him anywhere he wished to go, and when he arrived at Argos, he was welcomed as an honoured guest.
Unfortunately, Queen Anteia of Argos fell in love with the handsome young Bellerophon and tried to seduce him. When he rebuffed her advances, she had him sent to her father's kingdom, Lycia, where he was to deliver to King Iobates a message that, unbeknownst to him, was a plea from Anteia (Iobates' older daughter) to have him (Bellerophon) executed immediately. Fortunately for Bellerophon, Iobates was a clever man: he knew Anteia's licentious nature well, Bellerophon had managed to befriend the legendary Pegasus, and there was a resemblance between the young man and Poseidon, which meant it was likely he would incur the Sea God's wrath if he killed Bellerophon. Hence, he decided to try a different ruse: he tasked Bellerophon with slaying the Chimera, a supernatural monster who was terrorising his kingdom at that time.
Being ignorant of Iobates' true intentions, Bellerophon felt highly honoured by the task, and was determined to succeed. When he saw the Chimera while riding on Pegasus, he recognised its fire-breathing goat-head as its most dangerous aspect, and came up with the idea of choking the goat-head: after impaling a pillow-sized lump of lead on his spear, he managed to shove it down the goat-head's throat, which caused the Chimera as a whole to writhe with pain. While the Chimera was distracted, Bellerophon jumped from Pegasus and drove his sword through the monster's stomach, killing it.
Torn between an increasing fondness for Bellerophon and his unwillingness to deny Anteia's wishes, Iobates gave him a second task of subduing the Solymoi, a neighbouring tribe that was blessed by Ares, and often attacked the eastern border of Argos. Having found his self-confidence through defeating the Chimera, Bellerophon accepted the task willingly, and flew off on Pegasus to confront the Solymoi. When he returned victorious, Iobates gave him a third final task of defeating the Amazons and, when he succeeded, the remorseful king confessed his and Anteia's schemes, and begged for forgiveness, which the hero granted. Iobates was so grateful that he gave Bellerophon his beautiful younger daughter, Philonoe, to be his wife, and named him the heir to his throne.
King Bellerophon and Queen Philonoe had a good life together, but after many years of kingship, he became restless and longed for the old times where he wandered the lands on Pegasus, and was a hero idolised by all. Deciding that he needed one more adventure to prove his heroism and to gratify his need for excitement, he rode Pegasus to Olympus itself, intending to visit the gods. Unknown to him, mortals were not allowed entry on Olympus without special permission, and Zeus was therefore understandably enraged when he saw him. The King of Gods then fashioned a gadfly out of vapour, and sent it to sting Pegasus, causing the horse to rear, throwing Bellerophon off and causing the demigod to fall to his death.
- Prowess in Battle: After he had found his self-confidence, Bellerophon proved to be one of the greatest warriors of his time. He slaughtered half of the Solymoi, a tribe of fearless warriors who had never been conquered, and he later killed hundreds of the best Amazon warriors all by himself.
- Hydrokinesis (possibly): As a son of Poseidon, it is reasonable and logical to deduce that Bellerophon has the ability to control and manipulate water, though it was never revealed or confirmed as to whether he truly possessed this ability.
- Control of Horses (possibly): It is possible that, as a son of Poseidon, Bellerophon had the ability to control and communicate with horses, given Pegasus' surprising compliance in letting him put the magical bridle on it, and how he was able to communicate with Pegasus.
In Percy Jackson's Greek Heroes, Bellerophon was described to be a handsome young man who resembled his father, Poseidon. As demonstrated by Anteia and Philonoe, his looks attract female attention.
Bellerophon, like all demigods, is ADHD and dyslexic. He is also described to be exceptionally clumsy, as he killed his own brother and an innocent man unintentionally. He also has good morals as he rebuffed the queen's flirting, knowing his limits as a guest and sticking to them.