1. Kartikeya’s Anger
According to the Bhavishya Purana, once Lord Kartikeya was writing a book on the qualities of men and women. Ganesha interrupted him, which made Kartikeya angry. In his rage, Kartikeya broke one of Ganesha’s teeth. Later, Kartikeya returned the tooth to Ganesha after Lord Shiva’s advice and warned him never to separate it again.
2. Battle with Parashurama
The most widely accepted story comes from the Ganesha Purana. Once, Parashurama came to Kailash to meet Lord Shiva after defeating Kartavirya Arjuna. But Ganesha, following Shiva’s orders, stopped him at the gate. A fierce battle broke out, and though Ganesha overpowered him, Parashurama was forced to use his axe (a gift from Lord Shiva). The axe struck his tusk, breaking it. From then on, he became known as Ekadanta.
3. Fight with Gajmukhasur
According to another legend, a demon named Gajmukhasur had a boon that no weapon could kill him. He started troubling sages and saints, so Lord Ganesha fought him. Since no weapon worked, Ganesha broke one of his own tusks and used it to defeat and control the demon.
4. Writing the Mahabharata
The most famous story is connected with the Mahabharata. When Sage Ved Vyasa requested Ganesha to write down the epic, Ganesha agreed on the condition that Vyasa would not pause while reciting. Vyasa put forth another condition that Ganesha should write only after fully understanding the verses. As the narration went on, Ganesha’s pen broke. To keep the promise and avoid any interruption, he broke off one of his tusks and used it as a pen to continue writing the Mahabharata.