Ortiz began his martial arts career as a wrestler in his sophomore year of high school. Under coach Paul Herrera, Ortiz would place 4th in the state high school championships as a senior. Following high school, Ortiz continued his wrestling career winning a California state junior college title for Golden West College. Following his stint at Golden West, Ortiz wrestled at Cal State Bakersfield. While never a full-time starter, Ortiz did gain significant experience training with future NCAA and world champion Stephen Neal.

His mixed martial arts debut was at UFC 13 in 1997. Still in college, Ortiz competed as an amateur for no prize money or contracts. He beat Wes Albittron on the tournament's first round by referee stoppage due to a barrage of punches, but lost in the next round to Guy Mezger in a bout that he was dominating early on. The Mezger match showed the potential Ortiz had for dominating his opponents with control and hard, sharp elbows (ground and pound).

After returning with TKO victories over Jeremy Screeton at West Coast NHB Championships 1, and Jerry Bohlander at UFC 18, Ortiz dominated a rematch with Mezger. This time, the much smaller Mezger was out-wrestled, with Ortiz winning by TKO due to strikes. After winning the fight, Ortiz put on a t-shirt that read "Gay Mezger Is My Bitch" and gave the assembled Lion's Den, with whom Mezger trained, the finger (both fingers). Thus began both his rivalry with Ken Shamrock and the Lion's Den, as well as his custom of wearing t-shirts that belittled his opponent after victories or express his strong democratic political views (his UFC 51 t-shirt stated "Bring Home Our Troops- Get out of Iraq!)

In 1999 Ortiz fought Frank Shamrock for the UFC Middleweight (200 pound) title at UFC 22, losing what turned out to be an epic match via submission due to strikes. Following the victory, Shamrock retired and vacated the championship. The Middleweight title was renamed the Light Heavyweight title and Ortiz was chosen along with Wanderlei Silva as the top contenders. Their title fight at UFC 25 left Ortiz the champion via unanimous decision. Ortiz would successfully defend the belt five times in the following three years, defeating Yuki Kondo, Evan Tanner, Elvis Sinosic, Vladimir Matyushenko and Lion's Den head Ken Shamrock, who had held a grudge with Ortiz since the Mezger incident.

When it was time for Chuck Liddell to get his title shot (a then rising star in the UFC and #1 light heavyweight contender), Ortiz began a hiatus from title defenses. Ortiz had previously publicly challenged Liddell but now claimed that he and Liddell were friends and claimed a pact was made stating that they would never fight one another. Ortiz also expressed dissatisfaction with his contract with the UFC and they could not come to terms. An exasperated UFC management created an Interim Light Heavyweight Title to coax Ortiz to a fight. He finally agreed to fight the new Interim Light Heavyweight Champion Randy Couture, who had defeated Liddell for the interim title, at UFC 43 in September 2003. Although many had felt Couture was near retirement, he dominated almost the entire bout, winning via unanimous decision.

Following his loss to Randy Couture, Ortiz finally faced Chuck Liddell at UFC 47. Ortiz lost in a one-sided match by second round knockout. After six months off, Ortiz returned and took a unanimous decision victory over Patrick Cote at UFC 50, and a controversial split decision over Vitor Belfort at UFC 51. In February 2005, contract issues left Ortiz on bad terms with the UFC and its president Dana White, (who was also Ortiz' former business manager). During this time away from the UFC, Ortiz was offered deals with several promotions, including PRIDE Fighting Championships and the Don King-backed World Fighting Alliance, but none came to fruition. Ortiz opted to try his hand at professional wrestling, signing with Total Nonstop Action Wrestling as a guest referee.

--Wikipedia