A man is known by the company he keeps

Origin
This form of the proverb first appeared in 1912.
Explanation
A person tends to associate with the people who are like him or her.People are similar in character to their friends. The quote literally means that if someone hangs out with intelligent people, he is also assumed to be intelligent. Likewise, if someone is mostly seen with the people having a bad impression, the person also gets a bad impression. In other words, it means that what your friends are, you become. Your friends play an important role in how people think about your personality and character. So you’d better be careful while making friends. It means that a man becomes what his or her friends are; if we keep good company, we become good; if we have bad friends then we will surely adopt their bad habits. If you want to know about a man, just find out who his friends are. An example of this is that if you go and stay in a perfume shop, your clothes will aquire good smell but instead, if you go to an iron smith’s shop your clothes will smell like iron.
Examples
Son, when you go away to school, spend your time with serious people; don’t hang around with the people who go to parties all the time. A man is known by the company he keeps.
If you want to know what kind of person George is, look at his friends. A man is known by the company he keeps.