But he became best known as the everyday catcher of the 1944 Reds. In , Mueller had warmed up for his iron-man role by catching in 141 games for Cincinnati, including every game from July 31 through the end of the campaign. Then, in 1944, he started and caught in every Red game — 155, including an official contest that was ruled a tie. While he did not catch every inning for the 1944 Reds (backups Len Rice, Joe Just and Johnny Riddle handled 17 total chances in a total of 43 innings caught), Mueller caught 140 complete games and 1,329 innings; he handled 545 chances, threw out 39 percent of would-be base-stealers, and batted a career-high .286 with ten home runs and 73 runs batted in. He was named to the National League All-Star team and caught Clyde Shoun's no-hitter against Boston on May 15, 1944.