The fact that probably millions of people would vote for him to be president is terrifying to me.
We've had numerous celebrity politicians before Trump. Franken, Reagan, Arnold, Ventura, Springer, etc... The list continues[1] and it definitely wasn't Trump that was the first (although he holds the highest position of any of the other celebrity-actor-politicians, without having first held another political position).
[1] https://en.wikipedia.org/wiki/List_of_actor-politicians#USA
EDIT: Clarified my comment on Trump being the "first" celebrity-president
Zuckerberg strikes me as hell-bent on global domination, but doing it with the most plastic smile possible. Given any sort of real authority, I doubt even humor at his expense would go unchecked.