Bala

You already know that Aditi was married to the sage Kashyapa and that Aditi’s sons were the adityas or gods.
But the sage Kashyapa had another wife named Diti and Diti’s sons were the daityas or demons. The gods fought with the demons and killed several of them. In particular, Vishnu was responsible for killing many of Diti’s children.

Diti went and complained to Kashyapa. “My children are being killed by the gods,” she said. “Please grant me a son who will be strong and powerful and a source of joy to me.”

Kashyapa agreed. Diti meditated for a hundred years and gave birth to a son named Bala. (The word bala means strength.)

Kashyapa taught Bala the Vedas and various other shastras. When her son had grown up, Diti told Bala, “Several of my sons have been killed by the gods. I am thirsting for revenge. Defeat the gods. I particularly hate Vishnu I want you to kill him.”

Prior to doing this, Bala thought that he ought to obtain some powers by performing tapasya. He went to the banks of the river Sindhu (Indus) to meditate. Aditi got to know about this and warned her son Indra that Bala was meditating so as to become powerful. Once he accomplished this, it would be difficult to defeat him. If something was to be done, it should be done right away.

Indra has a wonderful weapon known as the vajra. (This is identified with the thunder. It is sometimes also identified as a club.) While Bala was meditating, Indra slew him with the vajra.

That was the end of Bala and also of Diti’s revenge.

Vritra

But Diti would not be denied. She went to Kashyapa and said, “My son Bala was meditating on the banks of the river Sindhu. That good-for-nothing sinner Indra has slain Bala while my son was meditating. Isn’t that grossly unfair? And aren’t you going to do something about it?”

Kashyapa agreed that it was unfair. He was furious that Indra had performed such a foul deed.