Loki
Loki has an attractive and persuasive personality which he uses to trick and deceive. He is vengeful, sly destructive and evil, but also handsome, resourceful, witty, sociable and possessing a great sense of humour.
He is a magician and shape shifter which allows him to fit in with any group. He also helped to construct both Asgard and the world of men.
Loki's contribution to the building of Asgard was the fact that he convinced a cunning giant to build a huge wall around the home of the gods as a defence against attack. The giant asked for the goddess Rreyja in return if he could finish the work in one Winter, and the gods agreed thinking that it would be a long time before the work was completed. The wall was constructed with great speed however and was nearly finished with Spring just a few days away.
The giant used a wonderous stallion to help him work on the wall so Loki took the shape of a mare and lured the stallion away from it's work. The giant failed to meet his deadline and Thor split his skull. The mare produced an eight legged foal who became 'Sleipnir' the mount of Odin.
So loki could be useful, but many of his acts were vindictive and meaningless. The gods eventually bound him in a special net and employed snakes to drip poison on him.
Adapted from 'A guide to the gods' by Richard Carlyon