He's the son of The Dagda and Boann, both of whom are married to other people. In fact, to hide their union, they made the sun stand still for nine months, allowing them to conceive and give birth to Aengus within the same day. Through the Dagda, he's the brother of Brigid, a triple goddess of fire, and the god Midir, who's also his foster father.
Consorts and Children:
While at war with Midir, he had an affair with Midir's second wife, Etain. He has a foster-son named Diarmuid, who was blessed with a birthmark that makes any woman who looks on him instantly fall in love.
Notable Stories Involving Him:
Also called Aengus the Young, he's described as being a young, handsome god with the ability to lull women with his harp-playing. His true love once appeared to him in a dream, after which time his mother began searching all of Ireland for her for a year, to no avail. His father then searched for a year, also with no luck. Finally, a king who was the Dagda's aide searched for a year, and was eventually triumphant. The king then led Aengus to a lake, Dragon's Mouth, where 150 maidens were chained up in pairs. Aengus instantly spotted the woman from his dreams, and learned her name was Caer. However, she and the other maidens transformed into swans on Samhain, all of them having been cursed to remain in that form until the next Samhain. So, in order to marry her, Aengus had to pick her out in swan form. Fortunately, he chose correctly, and joined her by turning into a swan himself. The two then flew off together, singing a song that put any who listened to it to sleep for three days and nights.
He's often accompanied by four birds, who constantly fly around his head. They represent the kisses used in love letters, and inspire love in all who hear their song.
Aengus Around the World:
He's the Celtic equivalent of the Roman god Cupid.
SOURCES: Wikipedia, Encyclopedia Mythica, & GodChecker