Dragons are very important and frequently met magical creatures.
They usually guard princesses who are locked up in the highest room of the tallest tower of their dragon's keep. Only the princesses' true love - a more or less handsome prince - is able to overpower the dragon's fierce portectiveness and live with the rescued lady happily ever after.
Dragons are in most cases very dangerous. They spit fire, their teeth are sharp as needles and their wings carry them over long distances; this enables them to chase potential intruders away - if they don't prefer to eat them. Dragons' eyes grant them a sharp sight and help these formidable guards of treasures detect the slightest change in their territory, which in most cases features a castle on a steep rock, surrounded by lava. Therefore it is not advisable to stir a dragon's fury - it might be the last thing for a daring knight or prince (or whoever) to to.
Fall asleep somewhere far, far away...