Is there a traditional "first Pagan" in Jewish texts? Related: were those killed in Noah’s Flood bad believers of God or nonbelievers?

I was thinking that post-Flood, you start with a population entirely of people who worship God, but sometime between then and Abraham, that’s apparently lost until God appears to Abraham. Is there a person generally considered to be the first one to stop believing in God? In the way that Ixion is the first kin-slayer in Greek mythology or Cain the first murderer?

Similarly, had this already happened pre-Flood? Is there a general consensus as to whether the wicked who were wiped out believed in God but were just sinful in other ways, or had they already abandoned belief in God?