Although General Pinochet was eventually allowed to return to Chile, it was Judge Garzon who in October 1998 helped convince the British authorities to arrest the general in the first place.
Most notably he spearheaded the campaign to extradite former Chilean Dictator General Augusto Pinochet from London to Spain for human rights abuses allegedly committed under his military regime.
Although General Pinochet was eventually allowed to return to Chile, it was Judge Garzon who in October 1998 helped convince the British authorities to arrest the general in the first place.
Judge Garzon continues to lead investigations into the former dictatorships of Chile and Argentina.
In the late 1990s he started by looking into the deaths of Spaniards in Argentina during the military regime of 1976-1983.
He eventually took on the Chilean case and studied the so-called Condor Plan, a scheme by South American dictators to help each other wipe out dissent.
It was on the basis of this plan that Judge Garzon charged General Pinochet and, later, 99 Argentines, with genocide.
They include Ricardo Miguel Cavallo, whom Judge Garzon is seeking to extradite from Mexico, where he was arrested in August after several people identified him as a former senior official of a torture centre in Argentina during the country's military regime from 1976-1983.
Political ambitions
Actions like this have put Judge Garzon on the international stage.
But he has also gained many enemies. A socialist, he gained prominence for his actions against the semi-official (GAL) death squads which operated in Spain's Basque region in the early 1980s.
That ended with the former Socialist Interior Minister, Jose Barrionuevo, in prison. But his impartiality is not questioned since he has also been active in Madrid's crackdown on the Basque separatist movement, ETA.
So much so that in early September the daily Spanish newspaper El Pais reported that ETA had recently plotted to murder the famous judge.
Then on 13 September, 19 suspected ETA members were arrested in a massive police operation on the group's political leadership. It was Judge Garzon who ordered the operation after a wave of summer assassinations and car bombings.
Judge Garzon is also known to harbour political ambitions and spent several months as a junior minister in a previous socialist government.
He walked out saying he was not being given the tools to do the job. But party sources said he was upset about being passed over for higher posts.