diogenes of Sinope (404–323 BC) was an active follower of the school of cynicism: the belief that the purpose of life is living in agreement with nature — using only the bare necessities.
Just like all other cynics, Diogenes rejected the things that were widely believed to make people happy: money, power, fame, and possessions. He criticized anyone who wasn’t temperate or honest. Cynicism was largely inspired by stoicism.
While he stood for his beliefs with great passion, he expressed them in a strange way. Rather than talking about his ideology, which was the standard way of philosophizing in ancient Greek times, Diogenes showed the world what he believed in through bizarre behavior.