Some information courtesy The Great Hisa's Puroresu Dojo (www.puroresu.com) and La Arena De Lucha Libre (www.highspots.com/arena/).
At first glance, Toryumon was a promotion started almost accidentally. Yoshihiro Asai, better known as the Ultimo Dragon, was wrestling for WCW at the time, the time being July 1998. During a match, he botched a fall he made on the recieving end of a spot, and ended up landing wrong on his left elbow. During operation by one of the WCW doctors, a nerve was accidentally cut which let to an infection of the elbow and a virtual uselessness of the arm. Asai was still sure he would be able to recover as he struggled to train his arm back to health.
Now, he couldn't wrestle at the time, but he still managed to be involved with the business in a big way. He had a gym in Naucalpan, Mexico, which was more or less his home when he was competing in the Lucha Libre feds away from his native Japan. There he also trained a number of other wrestlers, inclding Magnum TOKYO, Shima Nobunaga (later to be known as CIMA), Sumo Fuji, Judo SUWA, and the Dragon Kid. He trained them in the hybrid style known as lucharesu, which combines a lot of the lucha acrobatics with some of the stiffer impact from puroresu. And up until now he had also served as their road manager as well, getting them to work Japanese and Mexican freelance shows, Invitational Tourneys, and even brought them onto WCW TV for exhibition matches (in other words, matches where they'd job but learn to operate in front of larger crowds).
In late 1998 he made the announcement that he would be starting a fed with his students, to be based in Japan and to be known as Toryumon. Their first card was held on January 31, 1999 at Korakuen Hall in Tokyo. Since then, Toryumon has been building rapidly in popularity and in acclaim. It benefits from inter-promotion with the popular Michinoku Pro fed, as well as sending representatives to invitational tournaments where they well-represent the company, and working with Mexican federation IWRG (International Wrestling Revolution Group). In 2000, Toryumon started their first European promotion with the UK-based WrestlExpress, which was successful enough for them to establish a name in Europe that they'll be joining their shows this season as well.