A person who believes that
there is no God.
In contrast, an
Agnostic, which is someone who isn't convinced either way.
This
scientific-seeming belief may have come about out of disgust at the
superstitiousness of many
theistic religions.
Or, it may be because of
logical problems with the existence of God.
"
strong atheist" is an unnecessary term- we already have
atheist: There is no god
agnostic: I don't know / It's unknowable
Theist: There is a god