Peter Rosenthal has died several times. Once he died in court when his heart stopped. Each time doctors brought him back. Now he is dying a different death in front of a University of Toronto math class.

About 80 students sit quietly as the 72-year-old scribbles letters and numbers on the chalkboard. Some take notes, others fiddle on their phones.

“So the square root of two is irrational,” he says. “But what is the square root of two? What are the real numbers? Do you ever ask yourself that? Does it worry you?”

Silence.

Rosenthal has been working on a mathematical proof for an hour — showing that, in fact, the square root of two is an irrational number.

This is serious math, a second-year course the professor started decades ago called “Concepts in Abstract Mathematics.”

“So what do you think of that?” Rosenthal asks as he dusts chalk from his hands.

Silence.

“You’re a hard class to impress somehow,” he says with his wide, gap-toothed grin as the class breaks into tepid laughter. “Isn’t it nice to prove that?”

Silence.

“OK,” Rosenthal says in his gravelly voice as he clears his throat.

It is 8 p.m. on Wednesday with another hour of teaching to go. Rosenthal has been up since 5 a.m. working at his other job as a social justice lawyer. His name sounds familiar because many of his cases are high-profile, pitting little guys against big government or the police. He has made a life of questioning the rules, be they math formulas or laws most people follow without question.

He has defended 89-year-old census resister Audrey Tobias, G20 protesters, some of Dudley George’s siblings at Ipperwash where police shot and killed an unarmed George in a violent clash. He has altered election rules across the country, battled pharmaceutical companies and marched on Washington to hear Martin Luther King’s famous speech.

It’s really quite simple for Rosenthal: he views capitalism as the root of societal problems, and the powerful must be held to account. His next opportunity comes this week — closing arguments are likely coming on Jan. 8 and Jan. 9 in the inquest into several recent fatal shootings by police. Rosenthal, lawyer for the late Michael Eligon, will be one of those speaking.

He will work until he dies. And despite his heart problems, he’s well now and working, always working.

“Now here is a curious question with a curious answer,” he says as he turns back to the board.

The path to law

It has been a strange yet beautiful life for the New York City native, from rabble rouser to math professor to defence lawyer and back again. He walks a little slower now, and has great difficulties with his hearing, but his work continues.

He was a “red diaper baby,” the child of Marxist parents, whose ethos has guided his life.

“There should be economic equality in the world,” he says. “That would solve most, if not all, of the world’s problems.”

As such, he works for free for most of his clients. Math pays the bills.

Rosenthal got into law after being arrested outside the U.S. Consulate on University Ave. in 1969. The young math professor was giving a speech protesting America’s involvement in the Vietnam War when the head of the riot squad showed up.

“Get down off there,” the officer told him.

Rosenthal didn’t like that. So into the bullhorn he shouted: “He says I have to get down off here.”

“If you don’t get down, you’re going to be arrested,” the officer said.

“He says if you don’t get down from there, you’re going to be arrested,” Rosenthal repeated.

The officer dragged him down and cuffed him. They charged him with obstructing police and causing a disturbance. Then the cops on horses marched in and arrested 26 others.

He fought the charges because he believed he should be able to speak freely and “because having a criminal record would be a drag.”

He hired a young lawyer, Walter Fox, and began reading up on law. He badgered Fox so much — “ask him this” and “call this witness” — that his lawyer asked him during a recess whether he wanted to fight this alone.

Rosenthal did and fired Fox. He went on to get acquitted on one charge, but convicted on the other. He appealed that conviction and won.

He fell in love with law. “It was a funny process that I found fun,” he says.

He continued to protest and also took on friends’ cases as a paralegal, which allowed him to take on cases of minor criminal offences, including many acts of civil disobedience through the 1970s and 1980s.

During this time he befriended famed lawyer and activist Charlie Roach. The two became close. In the late 1970s, Roach asked Rosenthal to represent him — still just as a math professor — along with two others during a disciplinary proceeding in front of the law society. The society abandoned the prosecution after they made a motion to go to court.

Roach became pivotal in Rosenthal’s career arc.

“Charlie encouraged me to go to law school,” Rosenthal says. “Everyone else said it was ridiculous.”

But Rosenthal wanted to do things he couldn’t as a paralegal, which included serious criminal offences and representing clients on appeal.

“Whenever I lost, I wanted to almost always appeal it, but I couldn’t do that,” he says.

So he took the entrance test, which he aced, and was accepted into the law school at U of T. He managed to negotiate to remain a math professor while working towards his law degree.

In 1988, at the age of 47, he went back to school.

Taking on Tasers

At 12:30 p.m., Peter Rosenthal leaves the courtroom at the new coroner’s complex in Downsview, prepared to expose faults in a police officer’s testimony about Tasers later that afternoon.

He is there for an inquest into the shooting deaths of three mentally ill people, all of whom were holding a knife or scissors. It is a classic Rosenthal case: the powerless versus the powerful.

He represents the family of Michael Eligon, a 29-year-old Toronto father who had walked out of a hospital in February 2012, dressed only in his gown and socks. He grabbed two pairs of scissors from a convenience store and then asked a few strangers for keys to their cars.

Then the police arrived. Three shots later, Eligon was down, dead from the gun of an officer. The Special Investigations Unit examined and concluded police did nothing wrong. But Rosenthal completely disagrees.

Around 3:30 p.m., Rosenthal moves to the microphone at the inquest to cross-examine officer John Zeyen, who trains recruits on Tasers for the Ontario Police College. He speaks slowly and deliberately, dressed in his black pinstripe suit and black New Balance running shoes.

“Mr. Zeyen, you said earlier it would be rare to use a Taser in an “edge” situation. Is that fair?” Rosenthal asks, using the jargon “edge,” meaning a knife, scissors or the like.

“I’m never going to say never, but it would be rare,” Zeyen says, saying that officers are trained to draw their guns when facing a weapon.

With that, Rosenthal laid bare the “uselessness of Tasers” in any situation where officers feel threatened.

He has long been a fierce critic of police, telling the Star about forces’ “abuse of power” and “unchecked physical abuse.”

The Toronto police force has been a favourite target for Rosenthal. Do the police have any criticisms of Rosenthal?

“Not for publication,” said Toronto police spokesperson Mark Pugash in an email.

After court, Rosenthal folds himself into his Honda Accord, where he reflects on his career.

“I’ve done a few cases of people I’ve represented where I’m not convinced of their innocence and some corporate commercial clients,” he says. “Usually, it’s cases where I believe in their innocence or their cause.”

“My claim to fame is a case that went to the Supreme Court of Canada about the rights of small parties,” he says.

In that case, Rosenthal represented Miguel Figueroa, then the leader of the Communist Party of Canada, about the rights of small parties in Canada. His victory in the highest court changed election rules across the country.

He won that case based on fairness, a belief in always believing in treating people equally. On the drive south to his house, Rosenthal inches too far into an intersection when the light turns red, blocking the crosswalk.

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“Oh no, there is a woman in a wheelchair who wants to cross,” he says rolling down his window and apologizing. “This is not good, not good. Don’t report on my driving please.”

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Early struggles

Rosenthal was born to Harold and Esther in Flushing, part of the borough of Queens in New York City. He is very much a product of his parents — his father was a high school math teacher, and his mother a “flaming radical.”

At Flushing High School, he wanted to hang out with a crowd that didn’t like good grades, “so I appropriately did poorly in school.”

Despite his desire to fit in, he often didn’t. He faced some anti-Semitism that led to a fist fight in Grade 8. Despite his Jewish upbringing, he didn’t believe in God, which shocked a few of his teachers. He read one particular book, Jews Without Money, by Mike Gold, over and over.

But he also read and reread The Catcher in the Rye by J.D. Salinger. He liked Little Richard and Chuck Berry, but was “blown away by Elvis’s ‘Heartbreak Hotel.’ ”

He barely graduated and only had one option: Queens College.

Again he struggled at first, spending much of his time protesting civil rights and nuclear weapons rather than studying. He bombed the first calculus test in second semester.

So he began to care more for his studies and from then on excelled and fell for mathematics, working with prominent researchers that included Banesh Hoffman, who collaborated with Albert Einstein.

He married his high school sweetheart, Helen, in 1960.

“We were so young when we married,” he says, he 19, she 18. The couple had three sons and would later divorce in 1979. He married his current wife, Carol Kitai, in 1985, with whom he had a son and daughter.

His five children are very much a product of his beliefs.

“His view on capitalism is something he’s really passed down to his kids in a really positive way,” said his son, Michael, a musician.

Added his daughter, medical school student Esther, 24: “What I’ve taken from my dad is that there are many ways I can change the world and I’m going to try to do that through health care.”

From Queens College he went to the University of Michigan where he earned his master’s and doctoral degrees while studying operator theory on Hilbert space. When asked to describe that for readers, he said it’s about “transformations on a certain kind of infinite-dimensional space.”

“For people who get into math, it’s an especially beautiful subject,” he says. “I think of math and law as different sides of my personality. I could never give up both.”

After that he became a professor at the University of Toronto in 1967, drawn to the university for its reputation as well as for the city’s liberal views, which were perfect for his stand against the Vietnam War.

“I absolutely love Toronto,” he says. “I would never leave. There are many problems here that I’m trying to fix, but it’s a great, great place to live.”

Rosenthal’s closest academic collaborator is Heydar Radjavi, now an adjunct math professor at the University of Waterloo. The pair have produced more than 60 research articles since first meeting at U of T in 1967.

“He’s very inventive and creative and is fun to work with, which is important because a scientific profession can be frustrating most of the time,” Radjavi says.

The two still get together for a week or two during the summer — Radjavi has to get Rosenthal to Waterloo to physically separate him from his legal duties, where they work on problems on the blackboard, on paper, trying to solve the “invariant subspace problem,” a problem now more than 50 years old.

Assessing the world

After driving home from the coroner’s office, Rosenthal stops off at his Little Italy home, where he lives with his wife, Kitai, a family doctor.

“I have to change into my professor clothes,” he says, disappearing upstairs for five minutes and returning in a white, button-down shirt with grey slacks and a different pair of running shoes.

He cares little for fancy clothes. The boxy, black pinstripe suit he wore to the inquest came from Moores, “one of those two-for-one deals, I think.”

He strolls down College St. toward campus.

“In general, the world is worse than it used to be,” he says, ducking into a sushi restaurant. “Economically, things are worse than they used to be. What’s even worse is that people don’t even hope that it can be better.”

He saw flashes of a rising in the “occupy” movement, which fought against the economic inequality in society.

“The fatal flaw with it is they had a notion of not really organizing and be ultra-democratic, not have any leadership, but something like that can’t function. They need political organizing.”

“Capitalism is the problem actually,” he says over miso soup. “As long as you have the world dominated by big corporations who are functioning to maximize their profit, then it’s going to be a world that is not very accommodating to most people and will run roughshod over the environment and climate and all these concerns, because they’re just looking for the buck. To me that is sort of obviously true, but I wish it became obvious to a lot of people and then there was a real resistance.”

Health issues

Peter Rosenthal is aging. His hearing aids don’t work as well as he’d like. His heart, which has been fortified by a pacemaker in his chest, has stopped several times.

He plans to work until he dies.

In the fall of 2011, G20 protester Patrick Cadorette fired his lawyer and hired Rosenthal. But the Crown fought that move, saying Rosenthal would be in conflict because he represented another G20 protester, Jaggi Singh. The judge agreed.

He wanted to appeal, but he couldn’t because he was off the case. So he asked defence attorney Clayton Ruby to appeal on his behalf, which he won.

“Lawyers are to some extent cowed by judges and prosecutors and that issue is entirely absent from Peter’s personality,” Ruby says.

Rosenthal returned to court and began explaining how the judge sitting before him “made two critical errors.”

Suddenly, he grabbed the lectern, turned and slumped into a chair next to Cadorette. The courtroom was cleared while court officers rushed over to perform CPR and shock his heart back to life.

“It was really traumatic,” Cadorette says over the phone from Montreal. “Really, really tough to watch.”

“I have a vague memory of being on a gurney and being rolled out of the courthouse,” Rosenthal says. “Then waking up in the hospital.”

Doctors found significant blockages of several arteries that required angioplasty. But something went wrong during that procedure when one artery began bleeding. He was again near death, but lucid.

“I think there might be a problem,” he recalls the doctor saying.

“I came out of it a total mess, physically and mentally,” he says, unable to work as he recovered.

As he approaches campus for his math class, he needs a break from the legal talk, the talk of fighting for the little guy.

“Is it OK if we stop talking for a few minutes?” he asks. “I need five minutes to think about math and what I’m going to teach.”

The sun sets as Rosenthal walks along a leafy sidewalk in silence, the beauty of mathematics filling his head.