Ganesh Chaturthi is celebrated on the birthday of Lord Ganesh, the god of wisdom and prosperity. He is the son of Lord Shiva and Goddess Parvati. According to legend, Parvati created Ganesha from the sandalwood dough and breathed life into him (which she could by using her powers as a Goddess). She then asked him to guard the door to her house and instructed him to allow no one inside while her husband Shiva was away. When Shiva returned he was refused entry into the house by Ganesha (who had never seen him; and was merely following instructions of his mother). This angered Shiva drew his sword and beheaded Ganesha. Parvati, on learning that her son was beheaded, was enraged and asked Shiva to immediately revive him by replacing his head with the first living thing that he found in the forest. The first animal that Shiva found was an elephant; he cut-off his head and fixed it on the body of Ganesha to revive him.
Ganesha is considered the God of Good Luck and Prosperity and is the Dispeller of problems and obstacles. He is also worshipped as the God of knowledge, wisdom, health, fertility, wealth and happiness.