Doraemon is sent back in time by a young boy named Sewashi Nobi to improve the circumstances of his great-great-grandfather, Nobita, so that his descendants may enjoy a better future. In the original timeline, Nobita experienced nothing but misery and misfortune manifested in the form of very poor grades and bullying throughout his life. This culminates in the burning down of a future business he sets up which leaves his family line beset with financial problems. In order to alter history and better the Nobi family's fortunes, Sewashi initially wanted to send a super-robot to protect Nobita, but with his meager allowance he could only afford an imperfectly-made factory-rejected toy: an anthropomorphic robot cat called Doraemon.
Doraemon has a pocket from which he produces toys, medicines, and tools from the future, all of which are referred to as 'gadgets' by Doraemon. Some of the gadgets are based on real Japanese household devices with fanciful twists, but most are completely science fiction. Thousands of gadgets have been featured in the series with such as the "bamboo-copter", a small head accessory that allows flight and the "Anywhere Door", a door that opens up to any place the user wishes. (Source: Wikipedia)