One sees them in the centre of any major city -- the corps of the mentally ill, the sad cases who wander the asphalt pathways of urban green spaces. Downtown residents come to be familiar with their quirks, such as the bearded man who sometimes startles dog walkers as he berates the garbage cans of Trinity Bellwoods Park, or the leather-coat-clad pedestrian who trudges up and down Yonge Street waving her hands before her face, as if to ward off invisible insects.

Gordon Singer used to be one of these people. Now, he works to help them.

Mr. Singer, 46, has schizophrenia. He is also a peer-support worker for an assertive community treatment team at St. Michael's Hospital. ACT teams care for mentally ill people who are well enough to live on their own but who still require support to lead full lives.

Typically, each ACT team of about 14 members includes several psychiatrists and nurses, as well as specialized staff such as addiction counsellors and occupational therapists, and about 80 clients. Rather than expecting their patients to visit them, the teams go to the patients -- in a hostel, a halfway house or a city park -- to make sure they're taking their medication. Ideally, every ACT team -- there are 13 around Toronto, and more than 60 across Ontario -- has someone like Mr. Singer. "We look at more than their illnesses," he says. "We look at their lives as a whole."

Mr. Singer links the team and its clients. His job comes down to helping a client rejoin society. Often, someone who has been plagued with mental illness for most of his or her adult life hasn't learned to deal with the menial tasks that many of us regard as nuisances. For example, writing a cheque is frustrating. Doing laundry is a thorny exercise in algorithmic thinking -- first the detergent, then fill the machine with water, then the clothes. And for someone who has been in hospital for much of the past several decades, working out the cross-town trip from home to the dentist's office can seem impossibly confusing.

So Mr. Singer helps the ACT team's roster learn these sorts of tasks. He is good at his job because he's able to remember his own travails -- how intimidating he found buying tickets for the TTC, for example, or refilling a prescription at a pharmacy.

"He's done tremendously well for himself, and for others," says Rosza Gyulay, a case manager at the Centre for Addiction and Mental Health, who has known Mr. Singer for more than a decade. "When someone has schizophrenia, it takes a long time to trust yourself again. But Gordon never gave up his dreams. And now he helps people who were in a position similar to what he was in. He understands what his clients are going through."

This week, Mr. Singer braved the slush canals of downtown's sidewalks to discuss with a University of Toronto sociology class the illness that has plagued him for the past three decades. He wears his typical neat ensemble: a lime-green dress shirt tucked into a pair of sand-coloured cords, with black leather shoes stained with winter salt.

At 46, Mr. Singer betrays few of the side effects that have plagued some people who take the class of medication he is on. There isn't any Parkinson's-like limb shaking, for example. He doesn't work his jaws as though he's perpetually chewing a tough piece of meat. Nor do his thoughts seem jumbled.

What one notices when speaking with him is the precision of his speech. There is a formal quality to it, an absence of contractions or slang, and a calmness that brings to mind the computer Hal from Stanley Kubrick's 2001: A Space Odyssey. Occasionally, especially when he's tired, Mr. Singer repeats himself.

In front of about a dozen students, a professor introduces Mr. Singer. He stands, arms hanging straight at his sides, shoulders hunched up toward his neck. Engaging each student with eye contact, he begins his presentation.

"When I was 17, I was diagnosed with schizophrenia," he says, pronouncing the word with a long vowel sound: schizo-phreeenia.

His experience with the illness began earlier. Mr. Singer grew up in Sudbury, and his stint in high school was a study in loneliness. After a few of his long-time friends moved away, he began a progressive social withdrawal that resulted in almost total isolation from people his own age. Mr. Singer attended school but didn't talk to anyone. At home, he spent much of his time worrying about maintaining his 90-percentile average.

The solitude seemed to breed strange sights. The young Mr. Singer began to see light shooting from the eye sockets of certain people. He concluded that these people were, in some way, special. One day in 1974, at 17, he went to school and couldn't find his locker. His confusion escalated to almost total disorientation. "It was like a hurricane had run through my life," he says.

His parents took him to his family physician, who couldn't find anything wrong. After four more visits that week, the physician admitted Mr. Singer to a local sanatorium.

"I thought I'd be in there forever," says Mr. Singer, who soon moved to a Toronto hospital. He went on medication, but the delusions persisted: He heard voices almost constantly; their hostile words affected his self-esteem and made it difficult to concentrate.

During the ensuing 19 years, he would be admitted to hospital 15 times, he tells the students, sometimes for as long as a year.

One of the greatest difficulties was the way the illness sapped his motivation. "Imagine what it feels like when you don't want to get out of bed in the morning," Mr. Singer tells the class. "And then multiply that by 10 or 20 times."

Still, he displayed a remarkable discipline throughout his malady. In the eighties, he began taking courses at the University of Toronto. Although his hospital stays sometimes prevented him from completing a class, he says he has 12 of the 15 credits required for a degree in psychology. He has also been a member of Mensa for more than a decade.

Mr. Singer got his life back in 1993, when he began taking a new generation of anti-psychotic medication called Risperdal. Within a week, the voices stopped. And then began his inexorable reunion with society. He joined the board of directors for his housing co-op. The next year, the Centre for Addiction and Mental Health hired Mr. Singer to run its consumer advisory group, a group of clients who worked with the centre to improve its care. For the past four years, he has worked on St. Mike's ACT team.

After his U of T presentation, Mr. Singer sits in a Tim Hortons with a coffee cup before him. "In the eighties, a psychiatrist told my dad I'd probably have to be institutionalized for the rest of my life," he says.

Today, when he's not helping to care for the mentally ill population of central Toronto, he volunteers for several health-related organizations. He lives alone in a downtown apartment, and in his spare time he listens to music and reads a lot -- novels mostly. Graham Swift's Booker Prize-winning Last Orders is a particular favourite.

Does he struggle with the symptoms of schizophrenia any more? Sometimes, he admits, such as with a lack of motivation. "I'd still like to have more energy, more drive to do things," he says -- although he certainly seems to be doing fine with the energy he has.