Guillermo "Memo" Luna Romero (June 25, 1930 – November 9, 2021[1]) was a Mexican professional baseball player, a left-handed pitcher whose career extended from 1949 through 1961[2] and who pitched one game of Major League Baseball for the 1954 St. Louis Cardinals.

In 1951, he led the Class C Southwest International League in strikeouts (318)[3] and earned run average (2.52)[3] while posting a 26–13 won–lost record[2] for the sixth-place Tijuana Potros.

Two years later, Luna led the Open-Classification Pacific Coast League in earned run average (2.67),[3] as he won 17 of 29 decisions[2] for the 1953 San Diego Padres.

Luna started the Redbirds' sixth contest of the season, at Busch Stadium against the Cincinnati Redlegs, but he faced only six batters in the top of the first inning.

With two outs and the bases empty, however, Luna gave up another double, to Ted Kluszewski, and another walk, to Johnny Temple.