In the United States, he worked with NWA Total Nonstop Action (where he was part of the promotion's first match) or Ring of Honor, but most notably with World Wrestling Entertainment, where he had three different stints from 2001 to 2002, 2003 to 2005 and 2006 to 2010.

[8] In June 1999, Yun signed with World Championship Wrestling, making his WCW television debut in January 2000 under the ring name "Jimmy Yang".

[2] On April 13, 2002, Yun, competing as Yang, teamed up with Kaz Hayashi and Hi69 to defeat Kazushi Miyamoto, Gran Naniwa, and Ryuji Hijikata.

[2] On July 17 on an AJPW pay-per-view, Yang teamed up with Hayashi and George Hines to defeat Ryuji Hijikata, Gran Naniwa, and Johnny Smith.

[22] In September 2003, following a match with Tommy Dreamer on Sunday Night Heat,[4] Yun was signed to a three-year developmental deal with the renamed World Wrestling Entertainment (WWE).

This left Yun on his own to become a lower card wrestler and Velocity mainstay, competing primarily in the cruiserweight division until he was released on July 5, 2005.

[28] Yun stayed with the company for several months, wrestling as Jimmy Yang and using the same martial arts based persona he adopted in WCW.

In May 2006, Yun made a return to WWE, as Akio, on an edition of Heat, working as an enhancement talent in a try-out match with Charlie Haas.

Beginning with the August 25, 2006 edition of SmackDown!, vignettes began airing featuring Yun dressed as a cowboy and calling himself Jimmy Wang Yang, in the process cutting his previously long hair short and growing a Fu Manchu moustache to fit the gimmick.

In the vignettes, Yang questioned why people would assume stereotypical Asian things about him while proclaiming that he was much more of a redneck, of which he was proud.

On the September 29 SmackDown!, he made his in-ring debut in a loss to Sylvan, who illegally used the ropes for leverage to get a pin.

[35] During The Great American Bash, Yang competed in another Cruiserweight Open and although he was never pinned, Hornswoggle won the title after becoming an official entrant in the match due to him hiding under the ring.

[40] The following week, in a Fifteen Minutes of Fame Match, Moore and Yang tied the champions on pinfalls, resulting in Miz and Morrison retaining the titles.

[43] In September 2009, Yun sustained cuts and bruises to his back from Kane after being attacked with a Singapore cane on an episode of WWE Superstars.

[46] On the January 14, 2010 episode of Superstars, Yang and J scored their first win as a team after they defeated Mike Knox and Charlie Haas.

[49] In May 2010, after being released by WWE, Yun returned to the independent circuit as Jimmy Yang and was announced to be part of the new HighSpots Pro Wrestling Superstars talent booking roster.

[51] Yang finished second in his block, after victories over Shuji Kondo, MAZADA and Taka Michinoku, and advanced to the semifinals of the tournament.

[51][52][53] On August 8 Yang first defeated Minoru in the semifinals and then KAI in the finals to win the 2010 Junior Heavyweight League.