Jon Snow is a character in "Game of Thrones"
John Snow was a 19th century English physician who pioneered the use of anesthesia and hygiene in surgery.
Also, though I'm sure it's not relevant, John Snow was very coincidentally one of my ancestors from about 300 years ago.
I really hate it that Duo uses "exceptional" words like ничего. It's defined as a pronoun (standing for what? Who knows!) It's nominative form is ничто, so it doesn't seem to follow declension table in a regular way.
It's an excellent word to know - just not yet. Teaching exceptions before you teach basic rules seems counter-productive to me.