Ganesh Chathurti is celebrated as the birthday of Lord Ganesha, the son of Lord Shiva and Goddess Parvati. He is the symbol of wisdom, prosperity and good fortune.
Story of his birth
The son of Lord Shiva and Goddess Parvati, Ganesha has a unique story behind his birth. One day Goddess Parvati wanted to take a bath and Lord Shiva wasn't there to guard the door for her. As there was no one, she made a structure out of the turmeric paste she used to clean her body with, and put life into it. And hence was born Ganesha.
Elephant Head
Ganesha didn't always have an elephant head, he infact had a normal human head. One day when goddess Parvati was going to take bath, she told Ganesha to guard the door and he was so loyal that when Lord Shiva showed up, he even stopped him from entering.
At the time, Ganesha didn't know who Lord Shiva was. Lord Shiva also didn't know who Ganesha was and got really furious and ended up beheading him. When Parvati came out, she lashed out at Lord Shiva and threatened to destroy the universe, if he didn't bring back Ganesha.
Shiva realised his mistake and sent his troops into the forest to get the head of the first animal they saw in the forest. The troops came across an elephant and brought his head which was then placed over Ganesha's body. And thus Ganesha came to be known as the god with an elephant head- son of Lord Shiva and Goddess Parvati.
Ganesha and his one tusk
Ganesha is also called by the name 'Ekdant' which literally translates to one tooth. There are two stories behind this. One story suggests that he lost one of his tusks when sage Parshuram got into a fight with him. The sage was angry at Ganesha for not letting him meet Lord Shiva, while he was guarding the door.
Another story suggests that Ved Vyas (creator of Mahabharata) approached Ganesha to write down Mahabharata for him, he agreed but kept a condition that Vyas had to narrate it in one go, without any break. As he started writing the story, there was one point when the quill he was writing with broke down and without wasting any time, he broke off one of his tusks and made it into a pen to continue writing.