Santiago Rosario (July 25, 1939 – September 6, 2013) was a first baseman and corner outfielder in Major League Baseball who played briefly for the Kansas City Athletics during the 1965 season. Listed at 5' 11", 165 lb., Rosario batted and threw left handed. He was born in Guayanilla, Puerto Rico.

At age 20 Rosario was selected for the baseball team that represented Puerto Rico at the 1959 Pan American Games held in Chicago, Illinois. This was a historical fact because it was the first time that a Puerto Rico baseball team participated in the Pan Am Games. ′′Chago′′, as his teammates dubbed him, helped offensively and defensively his team, which won a silver medal in the event as a runner-up for the Venezuelan squad.

Rosario was signed originally by the St. Louis Cardinals as an amateur free agent in 1960 and was sent to the Athletics in 1964. He hit a .235 batting average in 81 games for the Athletics, 47 of them in pinch-hitting duties.

He also spent parts of nine minor leagues spanning 1961–1971, collecting a .275 average with 49 home runs and 332 runs batted in through 1091 games. After that, he joined the Mexican League from 1973 through 1976, and also was a member of the Leones de Ponce Puerto Rican team that clinched the 1972 Caribbean Series.

Following his playing retirement, Rosario coached in the Puerto Rican league both for Ponce and the Indios de Mayagüez.

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