Elves are present in all Northern European folklore, and are either good elves, or bad gnomes. Usually described as tiny creatures, elves are immortal and can do magic. Elves are very kind, but they can be full of mischief!
Hundreds of years ago, the job of an elf was to protect our homes against evil forces. In addition, if you were nice, they would be good to you, and if you weren't...well, you're seeing the origins of the naughty and nice list right here! Although thank goodness they no longer have the habit of sitting on your head when you sleep to give you bad dreams. In Old English, the word for 'elf' is also part of the words for both hiccup and nightmare, both of which they were said to cause.
Elves liked to have a bowl of porridge left on the doorstep at night to keep them well-fed and happy, which is probably where we get the tradition of leaving a snack for Santa on Christmas Eve.
Elves started to creep into Christmas in the mid-19th century, traditionally helping Santa with making and delivering presents to children, with Scandinavian writers responsible for elves getting the good press they deserve at long last.
Modern Christmas elves help Santa to bring Christmas to life, and in addition to their job designing and making toys and games for children, they look after the reindeer and keep Santa's sleigh in tip top flying condition. They also have a tendency to make appearances in homes in the run up to Christmas (often on shelves, funnily enough!) where they make sure that children are well-behaved and report back to the man himself so that he can keep his list up to date.