Vishnu is one of the three great gods of Hinduism, together with Brahma and Shiva. People often describe the three as a set of jobs: Brahma makes the world, Shiva breaks it down, and Vishnu keeps it going. That is why Vishnu is called 'the Preserver' — the one who protects the world and puts it right when things go badly wrong.

The famous idea attached to Vishnu is the avatar. When the world is in trouble, Vishnu comes down and is born into it in another form — as a fish, as a boar, as a man. These forms are his avatars, and there are usually said to be ten. The two best known are Rama and Krishna, and many Hindus worship those forms directly. So if a student asks 'is Krishna the same as Vishnu?', the honest answer is: for many believers yes, Krishna is Vishnu in another body — but some traditions put Krishna first and treat Vishnu as the form, so people do differ on this, and it is worth being careful rather than flat.

In pictures he is usually blue-skinned with four arms, holding a conch shell, a disc, a club and a lotus. He often lies asleep on a giant snake floating on the ocean, or rides the eagle Garuda.

Write it with a capital V — it is a name. And note that the English word 'avatar', the little picture that stands for you online, comes straight out of this religious idea: a god taking a visible form to come into the world.