After working for an electric power company for a year after graduating high school, Shiro Koshinaka enrolled in the All Japan Pro Wrestling Dojo in August 1978, training under Giant Baba and Kazuharu Sonoda. After months of training, on March 5, 1979, he debuted against one of his trainers, Kazuharu Sonoda.
In 1984, Koshinaka went on an excursion to Mexico, wrestling as Samurai Shiro in Empresa Mexicana de la Lucha Libre, where in July, he lost a Hair vs. Hair match to El Satanico. While AJPW pushed Misawa, the man Koshinaka beat to win the Lou Thesz Cup the year before, as the second incarnation of Tiger Mask, Koshinaka was lingering in EMLL in Mexico. Frustrated, Koshinaka left AJPW in August 1985.
New Japan Pro-Wrestling (1985–2003)
After his excursion in Mexico, Koshinaka joined New Japan Pro-Wrestling in September 1985. On February 6, 1986, he defeated The Cobra in a tournament to become the inaugural IWGP Junior Heavyweight Champion. At the same time, NJPW was in a feud with the shoot-style UWF promotion, and Koshinaka was immediately put in a feud with Nobuhiko Takada, who at one time was Antonio Inoki's protégé, just like Koshinaka was Giant Baba's. Koshinaka lost the title to Takada on May 19, 1986, but regained the title exactly four months later on September 19, 1986.
While reigning as IWGP Junior Heavyweight Champion, he formed a tag team with Keiji Mutoh in a bid to win the IWGP Tag Team Championship, which was vacated by Tatsumi Fujinami and Kengo Kimura in February 1987. On March 20, 1987, Koshinaka and Mutoh defeated Takada and Akira Maeda to win the vacant titles, making Koshinaka a double champion, but the tag team title reign didn't last as he and Mutoh lost the titles to Takada and Maeda in a rematch nearly a week later, on March 26, 1987. On August 2, 1987, Koshinaka vacated the Junior Heavyweight title due to an ankle injury. When he returned that fall, Koshinaka slowly rebounded, but the rebound was big when he won the first Top of the Super Juniors league in 1988, defeating Hiroshi Hase, the reigning IWGP Junior Heavyweight Champion at the time, in the finals on February 7, 1988, earning him a title shot against Hase on March 19, 1988, but lost. He tried again to wrest the Junior Heavyweight title from Hase on May 8, 1988, but failed again. Finally, on June 24, 1988, the third time was the charm, as Koshinaka finally won his third and final IWGP Junior Heavyweight title from Owen Hart.
He would hold on to the title, before losing the title to Hase on March 16, 1989.
As a new decade began, Koshinaka graduated to the Heavyweight division. In August 1990, he went to Austria to Otto Wanz's Catch Wrestling Association to challenge Steve Wright for the CWA World Middleweight Championship, but failed, as he lost on the tenth round. Returning to Japan in September 1990, he was the very first opponent for Mutoh's alter-ego, The Great Muta, and also joined Tatsumi Fujinami's Dragon Bombers.
After Heisei Ishingun disbanded, Koshinaka rebounded and regained the IWGP Tag Team titles in March 1999, this time with Kensuke Sasaki. He and Sasaki held on to the belts until June 1999, when they lost the belts to The Mad Dogs. In the summer of 2000, AJPW and NJPW were working together after the Pro Wrestling Noah exodus nearly killed AJPW. This led Koshinaka to return to his home promotion after fifteen years. He took part in a tournament for the Triple Crown Heavyweight Championship that was vacated by Kenta Kobashi; he defeated Johnny Smith in the first round, but lost to Toshiaki Kawada in the semi-finals. In January 2003, Koshinaka's contract was not renewed by NJPW officials.
In 2008, Koshinaka made his debut in Hustle, defeating Genichiro Tenryu and breaking his winning streak. Koshinaka would start teaming up with Tenryu in order to help him to recover his motivation, and they joined the babyface faction Hustle Army shortly after. Koshinaka also formed a tag team with KG, acting as her mentor.
^Royal Duncan & Gary Will (2000). "Japan; Top of the Super Junior Heavyweight Champions". Wrestling Title Histories. Archeus Communications. p. 375. ISBN0-9698161-5-4.