First of all there was a writer involved. You know those guys who actually come up with the plot, the dialogue, the the sequence of events, all those little things that actually make a story. So at the very least Todd is co-creator with David Michelinie.
But I will grant that Venom's visual appeal is a large part of his popularity. Some would say most of it in fact. But how much of that was really Todd? Mike Zeck was the artist on Secret Wars and Ron Frenz was the artist on Amazing Spider-man when the black costume came about. So Todd had nothing to do with the foundation of Venom's design. So what exactly did the supposed 'creator of Venom' do?
He added teeth.
The man is considered THE creator of one of Marvel's most enduring characters because he added teeth.
Fucking teeth. What a genius.