1. John Mayberry (1972-1977, 21.8 WAR)
John Mayberry may have only spent six seasons with the Kansas City Royals, but he made a dramatic impact on the team’s fortunes. One of the top players when the Royals began to ascend the standings and become one of the top teams in the American League, Mayberry was a force for the Royals.
Stolen from the Astros for Lance Clemons and Jim York, Mayberry went on to appear in two All-Star games and received MVP votes in four of his six seasons with the Royals. He twice finished in the top ten on the MVP ballot, including his second place finish in 1975 when he finished behind Fred Lynn. That season, Mayberry put together a .291/.416/.547 batting line, slugging 34 home runs with 38 doubles.
Overall for the Royals, Mayberry produced a .261/.374/.448 batting line, slugging 143 home runs and 139 doubles. He ranks fifth all time in on base percentage, and is in the top ten in home runs, OPS and RBI. While he did not play for the Royals as long as some of the other players on this list, Mayberry was still their best first baseman, at least in terms of WAR.
Maybe it was because John Mayberry was overshadowed by players like George Brett and Frank White, but he seems to be a forgotten player in Royals lore. However, Mayberry was the best first baseman in Kansas City Royals history.