In which year, people found that sun is not the only star in the universe?

Question

It is a well-known fact now that the sun is one of the multiple stars in the universe.

But in which year people at least hypothesized the fact that we are living in a universe with multiple stars?

Answer 1

This belief is known as cosmic pluralism and was found among the ancient Greek philosophers:

After Anaximander opened the door to an infinite universe, a strong pluralist stance was adopted by the atomists, notably Leucippus, Democritus, and Epicurus.

Though this was the belief that stars had planets -- that is, were, like the sun, not just points of light but with satellites.