over Inoue, Shamrock joined the UFC and fought Kevin Jackson for the newly created UFC Middleweight Championship (later renamed the UFC Light Heavyweight Championship). Jackson had won the middleweight tournament at UFC 14 and was undefeated in MMA at the time, and was also the Olympic gold medalist in freestyle wrestling for the 1992 Summer Olympics. Despite being a heavy underdog, Shamrock armbarred Jackson in just 16 seconds to win the championship. Shamrock then made his first title defense against then undefeated Extreme Fighting champion Russian Igor Zinoviev at UFC 16. Zinoviev was a feared Russian kickboxer and sambo specialist who held wins over Mario Sperry and Enson Inoue. Shamrock shot a double leg takedown and slammed Zinoviev down so hard that it knocked him unconscious. Zinoviev suffered a broken collarbone and a fractured C-5 vertebra from the slam and had to be carried out on a stretcher. Zinoviev's fight with Shamrock forced him to retire permanently from mixed martial arts ending the Russian's career. Shamrock then defended his belt against Jeremy Horn at UFC 17, submitting him with a kneebar. In October 1998, Shamrock avenged his earlier loss to John Lober by beating him decisively in 7 minutes at UFC Brazil. In September 1999, Shamrock defended the UFC Middleweight Championship against future UFC Light Heavyweight Champion Tito Ortiz at UFC 22. Ortiz had exploded as a star after his confrontation with Shamrock's brother Ken and his Lion's Den camp at UFC 19. The bout was hyped as a grudge, as Shamrock was a former Lion's Den member who, according to the marketing, was out for revenge against Ortiz. However, this was not necessarily the case because Shamrock had left the Lion's Den on bad terms a year and a half earlier. Despite dominating his opponents in his previous title defenses, Shamrock was considered to be an underdog in this fight; Ortiz had come off convincing wins over Shamrock's former teammates Jerry Bohlander and Guy Mezger and popular opinion was that Ortiz was too big and strong for him to deal with (Ortiz cut weight to fight and by the time he stepped into the cage he would have on Shamrock). However, in what is widely considered to be one of the greatest fights in UFC history, Shamrock won after brutal elbows, punches, and hammer blows forced Ortiz to tap out at the end of round 4. Shamrock has stated