Is sleep time related to any other characteristic? Some people say that smart people sleep less, other say that smart people sleep more. I also heard that Napoleon used to sleep 4h/day.

Is sleep-time related to any other characteristics like intelligence, strength, etc. ?
Both sleep time, onset and duration have been correlated in various studies, some hard and some soft with intelligence.

This study suggests that the more intelligent people tend to be night owls, and stay up later in the day. This is somewhat related to intelligent people tending to seek out things that are not the "norm" for stimulation.

Related to that, is a theory that smart people need less sleep, as their brains are more efficient while they are asleep. This study bears that out, as a group of 60 children from 7 to 11 years old exhibited higher cognitive function when getting less sleep.

Both of these tend to bear out the perception that smart people sleep less. Napoleon is estimated to have an IQ of 145, using various estimations of accomplishments versus age.

Conversely, physical activity is known for needing higher amounts of sleep, and lack of sleep can impact both physical and mental recovery. This study with basketball players showed both mental and physical improvements with extended (10 hour) sleep periods. However, I could not find anything suggesting that stronger people slept more or less as a condition of being strong.