Once upon a time, there was a powerful demon by the name of Gajasura. He had the head of an elephant on a human body. One day, he started to perform intense penance towards Lord Shiva. After a long time, Lord Shiva appeared in front of him and asked him what his desire was. Gajasura said that he wanted to rule the universe and the gods in heaven should bow before him. After this, he said that only a being who was looking like him could defeat him. Lord Shiva heard all these wishes and granted them.
As you all would have guessed, Gajasura used his newly acquired powers to cause mayhem and wreak havoc in the three realms. People and gods ran scared from him and his trail was filled with destruction and death. Some gods then went to Lord Brahma and asked him for help. Lord Brahma informed them of the boons which Gajasura had and so he told them that only Lord Ganesha would be able to defeat him. So all of them went to Lord Ganesha and informed him of the situation. Lord Ganesha calmly said he would handle the situation and descended to earth.
Gajasura was wreaking havoc as usual and when the smoke of his destruction cleared, he was shocked to see someone looking like him standing in front of his eyes. Without a moment’s loss, he remembered the boon he had asked for and decided that it was best to kill him. So he took a weapon and hurled it towards Ganesha. He jumped and dodged the attack, which exploded behind him. Gajasura was beginning to grow frustrated and he drew out all sorts of weapons and attacked Ganesha with it. Ganesha demonstrated his skill as a warrior and he either dodged or tackled the weapons with expert skill. Now it was Ganesha’s turn and when he retaliated, he thrashed Gajasura black and blue with his bare fists and feet. Gajasura was on the verge of defeat.
Gajasura then transformed into a mouse and began to run. Ganesha leaped in a flash and caught hold of his tail. Gajasura immediately begged for his forgiveness and Ganesha forgave him for his sins. Ganesha then told Gajasura that he would henceforth be his vahana in the form of a rat.