He has put dictators, torturers, terrorists and drug barons in the dock. Now, he himself faces an extraordinary battery of criminal charges.

The already astonishing drama surrounding Spain's crusading "superjudge", Baltasar Garzón, hit a new peak as corruption was added to the charges against him and thousands of his supporters blocked streets around the supreme court in Madrid.

The continuing trials faced by Garzón over his controversial investigations into mass killings by the Francoist dictatorship and corruption in the ruling People's party (PP) have already seen his case compared to France's infamous Dreyfus affair. "This is deplorable and intolerable," said the Workers' Commissions trade union leader, Ignacio Fernández Toxo, at the demonstration.

But a fresh charge of taking bribes from Santander bank while on sabbatical at New York University, which has been angrily denied by Garzón and all those involved, has fuelled worries that the world's most famous human rights investigator is being subjected to a concerted campaign of persecution. "I am facing the firing squad, but I've asked them to take off the blindfold," the man who had Chile's General Augusto Pinochet arrested said in an aside during one of three trials he currently faces for alleged abuse of his powers.

On Tuesday, for the third week running, he returns to the supreme court, where he usually sits stern-faced in his black magistrate's robe with embroidered cuffs under a painted ceiling featuring child-throttlers and knife-wielding assassins.

He is accused of perverting the course of justice by opening an investigation into the fate of 114,000 people killed by Francisco Franco's regime. Garzón believes he will win his case on appeal, but has long been convinced supreme court judges are determined to declare him guilty and expel him from their ranks. "I hope justice will prevail, but it seems to me the prejudice is already there and that in any of the cases against me the verdict will be guilty," he told film-maker Justin Webster while waiting for the court to fix trial dates.

The zeal with which the supreme court has pursued the cases was highlighted this weekend when newspapers leaked the recommendation that corruption charges be brought. Supreme court judge Manuel Marchena alleged Garzón had abused his powers to extract sponsorship for courses, receiving money indirectly.

"I did not solicit, administer or receive, either personally or through third parties, directly or indirectly, money or gifts from the entities and corporations that sponsored the courses and seminars where I was academic director," Garzón replied. He is backed by the university.

Friends say that, beneath his cool facade, Garzón is going through private hell. "I do ask myself why I am here," he admitted during his first trial, accused of illegally wiretapping remand prisoners and their defence lawyers in the PP's "Gürtel" corruption scandal.

Global human rights activists ask the same question. "Garzón has made many enemies because he is a judge who causes problems," said Reed Brody, of Human Rights Watch. "But we need judges who cause problems, not ones who are subservient to power."

No Spanish investigating magistrate, who prepare cases rather than try them, has ever faced three such separate but simultaneous trials. Many see a conspiracy by jealous colleagues. "If it had been anyone other than Garzón, they would never have put him on trial," said a prosecutor who has worked closely with him.

Garzón got to this point, first and foremost, by poking a finger into one of Spain's most sensitive, gaping wounds. In October 2008 he opened an investigation into Francoist crimes. His decision swept aside a 1977 amnesty law and challenged a tacit accord that Spaniards should not argue over their bloody civil war or the 40-year dictatorship that ended only with Franco's death in 1975.

Garzón named Franco as one of 34 suspects. The superjudge was deliberately chasing ghosts, as all were dead. The move enraged conservatives, some of whom see Franco as little more than a benign authoritarian. "It [the Franco regime] was a period of extraordinary calm," claimed Jaime Mayor Oreja, a former PP interior minister. Garzón might as well put Napoleon on trial, declared Manuel Fraga, the party's founding president and a former Franco minister. "It is an outrage," he said. "There were amnesty laws."

But circumventing amnesty laws is just one speciality of a judge who shot to global fame in 1998 when he had Pinochet arrested so he could be extradited to Spain for the killing of 3,000 Chileans.

While many doubted that Garzón's unprecedented use of international human rights law, two law lords' rulings allowed for the extradition – effectively agreeing that Chile's amnesty laws allowed other countries to claim jurisdiction. The then Labour home secretary, Jack Straw, stopped the extradition by sending Pinochet home on what were widely seen to be politically convenient health grounds.

But a precedent was set. Some, indeed, see it as the most important human rights case since the Nuremberg trials, leaving practitioners of genocide and torture with nowhere to hide.

Garzón then had an Argentinian navy captain, Adolfo Scilingo, tried and jailed in Spain for crimes committed thousands of miles away – further extending the reach of international human rights law.

Judges in Chile and Argentina were emboldened by his actions and eventually struck out their amnesty laws. But historical memory campaigners, who seek out and dig up Franco's mass graves, say the case against Garzón means Spanish judges are now too scared to take the same path.

"Will Franco's victims have fewer rights than Pinochet's victims?" asked Brody. "Garzón is being tried for applying exactly the same principals he successfully defended in international law."

Even before the Pinochet case Garzón was a controversial, crusading figure in Spain. He took on state-sponsored terrorism in a dirty war against violent Basque separatists, falling out with a Socialist party that had briefly – and controversially – added him to its list of parliamentary deputies. Garzón also won massive public support for his pursuit of Galician drug clans and the armed Basque separatist group Eta, even shutting down newspapers and suspending political parties deemed to back terrorism.

The legend of the "superjudge" was born, though Garzón claims to dislike it. "It is not the judge who is the star," he said. "It is the case."

The left-leaning son of a petrol attendant from the poor, olive-growing southern town of Torres, he has always been an outsider. Garzón's father had insisted that, to get on, "you have to see the sun rise". By the time he was 32, he had become the youngest ever magistrate at the powerful national court.

But he has few friends in his courthouse. Only half a dozen judges and prosecutors walk the short distance from the national court to the supreme court to offer moral support before each of his trials.

When a tiny trade union called Clean Hands, which has links to the far right, presented a writ against him for opening the Francoism case, the disregard of many colleagues soon became clear.

"This writ opened the field against Garzón," said Clean Hands leader Miguel Bernad, formerly of the pro-Francoist National Front. "Because of his huge ego, he thought that after going against Chile and Argentina, he would apply universal justice here in Spain. But he is not impartial. He is only interested in rightwing regimes. All he wants is stardom and headlines."

Then a complaint was lodged by the lawyers wiretapped during the Gürtel investigation. The allegation that Garzón knowingly dictated a measure that was against the law, rather than simply interpreting the law in a way others might disagree with, is tough to prove.

Even those who think Garzón is a high-handed judge with a bloated ego agree that, were it not for the Franco investigation, he might have escaped prosecution in the other cases. "The real reason he is on trial is because of historical memory, not Gürtel or New York," said Italian author and economist Loretta Napoleoni, who has written a book about Garzón. "But the Gürtel case is quite shocking, because you just don't listen in to conversations in jail between lawyers and defendants."

Napoleoni believes the wild applause that greeted Garzón's pursuit of terrorism and organised crime went to his head and led him astray. "He is the fallen star. He has been sacrificed," she said.

Garzón has vowed to fight his cases as far as the European court of human rights. "If fear or cowardice take root in a judge, then society is lost," he said.