Juan Modesto Guilloto León (Puerto de Santa María , Cádiz, 1906-Prague, Czechoslovakia, 1968) was a Republican army officer during the Spanish Civil War.
He originally worked at a sawmill before joining the Spanish Army. He served in Morocco, becoming a sergeant major of the Legion. Affiliated with the Communist Party of Spain (PCE) from 1930. He was placed in charge of the Milicias Antifascistas Obreras y Campesinas (MAOC) of Madrid in 1933, which constituted a paramilitary force for the communist party. He organized the Sindicato de Oficios Varios y el Socorro Rojo. When the civil war exploded in July 1936, he participated in the assault of Cuartel de la Montaña and fought in the Madrilenian Mountain range. He was one of the heads of 5º Regiment (he commanded it from October 1936). He fought in Talavera de la Reina and Illescas (September 1936) and in the defense of Madrid, as well as in the battle of the Jarama (February 1937). He was promoted to lieutenant colonel of the popular army and command of 5º Army Corps, participating in the battles of Belchite, Brunete (July 1937) and Teruel (January 1937 and December 1938). In 1938 he was promoted to colonel and became head of the Army of the Ebro. After the fall of Catalonia to the Nationalist army, Negrín named him general and head of the Central Army on March 2, 1939, and in less than a month he left in an airplane on course to the Soviet Union, whose government recognized his military rank. During World War II he served with the Red Army and Bulgarian army. Defeated in the struggle with Jose Diaz for control of the PCE, he went to Prague.