Guillermo Montañez Naranjo (born April 1, 1948) is a Puerto Rican former professional baseball first baseman, who played in Major League Baseball (MLB) for the California Angels (1966), Philadelphia Phillies (1970–1975, 1982), San Francisco Giants (1975–1976), Atlanta Braves (1976–1977), New York Mets (1978–1979), Texas Rangers (1979), San Diego Padres (1980), Montreal Expos (1980–1981), and Pittsburgh Pirates (1981-1982).

On October 7, 1969, the Cardinals traded Curt Flood, Byron Browne, Joe Hoerner and Tim McCarver to the Philadelphia Phillies for Dick Allen, Jerry Johnson and Cookie Rojas.

When Curt Flood refused to report to his new team, the Cardinals sent Montañez and Jim Browning to the Phillies to complete the trade.

He finished second behind Atlanta Braves catcher Earl Williams in the National League Rookie of the Year balloting.

With Del Unser's arrival in Philadelphia in 1973, Montañez returned to his natural position at first base where he stayed for the remainder of his career.

Made expendable after the Phillies claimed Dick Allen off waivers from the Atlanta Braves one week earlier, he was traded to the San Francisco Giants for Garry Maddox on May 4, 1975.

[5] Montañez was dealt by the Braves to the New York Mets in the first four-team deal in Major League Baseball history on December 8, 1977 that also involved the Texas Rangers, Pittsburgh Pirates and a total of eleven players changing teams.

The Mets also got from the Rangers Tom Grieve and Ken Henderson who was sent to New York to complete the transaction three months later on March 15, 1978.

Following the season, he was traded to the San Diego Padres for Tucker Ashford, Joe Carroll and future Hall of Famer Gaylord Perry.