If by linguist you mean a person who loves and knows many languages (thus not always a specialist of linguistics), then the world's current best linguist is a Lebanese man who lives in Brasil named Ziad Fazah. Actually, the word polyglot is better but less used. The guy speaks, reads and understand more than 40 languages, most of them learned before he was 20!

He has been invited several times on TV shows and has been tested by speakers of such odd (please excuse me) languages as mongolian and hungarian, always with success.