Lord Ganesha saved the Gods when they were in trouble, by killing the demon Talasura and outwitting the demon Ravana. He is also worshipped as the God who grants success.
Lord Ganesha is the deity of auspiciousness. He is adorable not only to man but also to the Gods. The word 'Ganesha' means the Lord of Ganas (the army of the Gods), the leader of the army of Lord Shiva. That is why he is also called Ganapati and Gananayaka.