How so? Seriously, what makes you say that?
-The Game & Watch was Nintendo's first gaming
success and was a long, notable part of Nintendo's history.
-R.O.B. was the Trojan Horse that saved video games in the Western market during the Crash of '83.
Both are "revived" through various means as time goes on (G&W games continuously get rereleased on handheld systems, R.O.B. makes numerous cameos throughout Nintendo's series, etc.)
Sheriff? Complete lack of notability for Nintendo other than the thought that he is Nintendo's first actual "character", but the first "character" was really among a set of horse jockeys or race car drivers in EVR Race (the game Nintendo claims was their first) depending on which tapes were used. And then baseball players in EVR Baseball.
Also doesn't appear that often if at all in other games, with the only notable reference in the past decade being the remake Wario's Sheriff in the first WarioWare back in 2003.
So no, Sheriff cannot be compared to G&W and R.O.B. at all. No one really can.