What would you say is the minimum number of champions a player needs to know?

So let's just say you have an aspiring S10 Ranked player looking to climb to at least, ehh, Plat 4.

Let's also say this player has decent background knowledge of virtually every champion in the game. Not to any serious depth, but he does know what everyone generally does.

Now, as a human being that probably needs to eat, sleep, have a social life outside of the game, etc., he obviously can't go out of his way to main every single champion in the game. Too large of a time commitment, and too many champions for him to really be good at all of them anyway. But he does need to have a dedicated pool of champions that he knows intimately enough to push to their limits, and a large enough pool so he can play in as many matchups as possible without being locked out by bans and counter picks.

So with this in mind, how many champions does this hypothetical player need to know?

Answers vary based on your primary and secondary role so feel free to include roles in your answer if you want to answer for any specific combination (like a Bot/Supp main or a Top/Mid main). You can also go with general descriptions like generalists and safe ranged farmers, or you can highlight particular champions (I personally think everyone should learn Nunu since he's a reliable pick for Jungle mains and a safe and easy pick for Auto Filled Junglers).