This short list contains only the unquestioned greatest who played almost exclusively for that team:
St. Louis Cardinals: Stan Musial
New York Yankees: Babe Ruth
Boston Red Sox: Ted Williams
Braves: Hank Aaron
Philadelphia Phillies: Mike Schmidt
Detroit Tigers: Ty Cobb
Pittsburgh Pirates: Honus Wagner
No clear greatest: Reds, Cubs, Indians, Orioles, White Sox, Senators, Dodgers, Athletics, Giants.
The Giants were the most difficult: Willie Mays or Barry Bonds.
Johnny Bench leads the Reds in home runs and RBI but not much else. Pete Rose leads in WAR and more things than Bench.
Originally I had Ernie Banks for the Chicago Cubs. But when I checked, Sammy Sosa hit the most career Cub home runs, including the most in Wrigley Field, and Cap Anson leads in a bunch of stuff. Banks simply did not dominate.
Orioles: Cal Ripken leads only in totals. Not nearly as clear cut as the others I picked.