The Soviet probe that crashed on the Moon during Apollo 11’s lunar stay was Luna 15.
Luna 15 was an uncrewed Soviet sample-return mission launched on July 13, 1969, three days before Apollo 11. It entered lunar orbit on July 17 while the American spacecraft was still traveling toward the Moon. Its goal was to collect lunar soil and return it to Earth before Apollo 11 completed its mission.
After orbiting the Moon for several days, Luna 15 began its descent on July 21, while Neil Armstrong and Buzz Aldrin were completing their first moonwalk. Contact was lost shortly after the descent began, and the spacecraft crashed in Mare Crisium at about 15:50 UTC—hours before Apollo 11’s lunar module lifted off.
A common mix-up is Luna 16, which successfully returned lunar samples to Earth in 1970. Luna 15 was the earlier, unsuccessful attempt, and its parallel flight with Apollo 11 became one of the final episodes of the Space Race.