Tendermint consensus: Are validators "known" and "pre-selected"? What are similarities and differences between Tendermint consensus and Proof-of-Stak?

For example, in both consensus, a validator is selected randomly (I think in Tendermint consensus they are selected in a round robin process). 

And I think in Tendermint consensus, validators are known and pre-selected, unlike Proof-of-Stake consensus. Is it true? and if yes, what entity does confirm a known validator?
Yes they are known. They are selected via a round-robin fashion. The Tendermint team intend to add a VRF to randomly select validators:

https://github.com/tendermint/tendermint/issues/763