Sonam Tashi was a soldier in the service of the Maharaja of Katmandu. He and Patar Kali, accompanied Indiana Jones on the archaeologist's quest to find the Covenant of Buddha in 1938. While on a train going through Afghanistan, the group was attacked by Waziri bandits, who disconnected the rear cars, leaving Tashi and a team of sherpas unable to contact Jones or Kali. Tashi and the others were later attacked by Japanese general Masashi Kyojo and his soldiers. Tashi and a few of his men managed to escape, but others weren't as fortunate. However, Tashi managed to capture one of Kyojo's soldiers who, after being interrogated, revealed that there was a spy in the group.
Tashi met up with Kali and Jones after rescuing Sophia Hapgood, from the bandits who had attacked the train. After informing Jones and Kali of the attack, Tashi disguised himself as one of Kyojo's soldiers, and snuck into the Japanese camp. There he saw one of his sherpas entering the command tent. Once the sherpa emerged, Tashi dragged him into the woods, and stabbed the spy to death. Before Tashi could return to Kali, he was confronted by the katana-wielding, Sergeant Itaki, who promptly decapitated Tashi.