In Vedic times Indra was a weather god, in mythology he is the King of the Gods, son of sage Kashyapa. He is married to Sachi, also called Indrani.
In the Mahabharata he is the father of Arjuna.
Indra is a title, in every world age there is a new Indra.
As Devendra (Deva Indra) he is the Indra of the Gods.
He was cursed by the sage Gautama for seducing his wife, Ahalya. Indra’s body was covered by a thousand labia. One of the gods turned the labia into eyes, which is why he is also called the thousand-eyed.
His heroic deed was the destruction of the demon Vritra.
Read about Indra here