Who was not a member of the three dog night?

The question is a bit of a trick! "Three Dog Night" wasn't a person, it was a band.

The band's core members were:

* Cory Wells (lead vocals, guitar)

* Chuck Negron (lead vocals)

* Danny Hutton (lead vocals, guitar)

So, to answer your question, no single person was "not a member of Three Dog Night" because it's a band, not an individual.