Rubén was the son of the Communist politician Dolores Ibárruri, and her husband Julián Ruiz Gabiña. Among their six children, he and his sister Amaya were the only ones to become adults; four of his siblings died very young. While still a child, Ibárruri took part in political activities. When he was thirteen, he distributed illegal communist leaflets and had to evade the police. In 1935, after his mother was imprisoned, he and Amaya were sent to the Soviet Union. Rubén resided in Moscow with the Bolshevik leader Panteleimon Lepeshinsky and his wife, biologist Olga Lepeshinskaya. He took up an apprenticeship in the Joseph Stalin 1st State Factory for Automobiles.
After the outbreak of the Spanish Civil War, the sixteen-year-old Ibárruri approached the Spanish Embassy in Moscow under a pseudonym and - after lying about his age - volunteered to fight on the Republican side. He joined a Spanish Republican Armymountain infantry unit in Major Juan Modesto's corps. When General Alexander Rodimtsev met him in August 1937, he already held the rank of a corporal. After participating in the Battle of the Ebro, he was promoted to sergeant. During February 1939, Ibárruri crossed the Pyrenees into France, with the remnants of the defeated Republican Army, and was interned in the Argelès-sur-Mer concentration camp. He managed to escape and reach the Soviet Embassy in Paris, from where he returned to Moscow at April, reuniting with his mother and his sister. Ibárruri attempted to enroll into the Stalingrad Military Flight School, but was rejected on medical grounds. He then entered the Moscow All-Russian Central Executive Committee Military Academy. After graduation, Second Lieutenant Ibárruri was stationed in the machine-gun platoon of the Moscow 1st Proletarian Division's 175th Company.
In early July 1941, soon after Germany invaded the Soviet Union, the 1st Division confronted the enemy in the town of Borisov, near the Berezina River. Ibárruri's platoon covered the retreat of the regiment across the river. He was severely wounded during the battle, and evacuated to the Kuibyshev where he recovered and associated with Leonid Khrushchev who was also recovering there. In September 1941, President Mikhail Kalinin had personally awarded him the Order of the Red Banner. After recovering, Lieutenant Ibárruri joined the 35th Guards Rifle Division, which was formed from the 8th Airborne Corps in August 1942, as the commander of the 100th Machine Gun Company. The division was consigned to the 62nd Army, which defended Stalingrad. When arriving in the area, the division was rushed to the village of Samofalovka, 30 kilometres north-west of Stalingrad, to halt the advance of the German army toward the Volga River. By the night of 23 August 1942, only a part of the 35th reached the area. Ibárruri's battalion, commanded by Captain A.A. Stolyarov, was deployed in the Kotluban train station and immediately attacked by German forces. Stolyarov was killed in the fight, and Ibárruri replaced him, leading the soldiers while the rest of the division arrived. In the morning, he was hit by a bullet in the abdomen and sent to a field hospital in Srednyaya Akhtuba - a town on the other side of the Volga, 20 kilometres east of Stalingrad. He died from his wound on 3 September 1942. On 2 November 1948, his remains were re-buried in the Square of Fallen Heroes, on the Mamayev Kurgan. On 23 August 1956, he was posthumously awarded the title Hero of the Soviet Union. The asteroid 2423 Ibarruri was named in his honour at 1972.
