Ask William Charles Dement what his middle initial stands for, and he’ll tell you “Crusader.”

A little eccentric but always good-humored, the 79-year-old Medical School professor is an evangelist — just not for Jesus. Three times a week, for 50 minutes, he espouses his message like a revivalist preacher to a packed Kresge Auditorium.

“People are dying as I’m speaking whose lives could be saved by sleep knowledge,” said Dement. “We need to lower the floodgates or blow up the dam so knowledge can flow to people who need it.”

For almost four decades, he’s been teaching “Sleep and Dreams,” one of the most popular classes ever offered at Stanford. The first time, in the winter of 1971, he spoke from the pulpit in the stained glass-filled sanctuary of Memorial Church. By his estimate, more than 20,000 students have taken the class since.

He feels a calling to spread the gospel of slumber, as if the lives of his students depended on it.

“This may not seem like the highest intellectual level of teaching, but it’s why three people came up to me and told me I saved their lives,” he said last week, announcing to the class that he keeps a folder of letters from former patients who credited him for advice or treatment.

Driving while tired can be as bad, or worse, than driving while drunk, he tells students. Behind almost every major industrial failure, in his view, is someone deprived of sleep.

If students take away only one thing from the class, Dement insists that it be his creed, “Drowsiness is Red Alert.”

The idea is that someone is almost asleep when they start to feel the telltale signs of drowsiness. This fatigue should be taken as a final warning sign from a body desperate for rest. If you’re driving and start to feel drowsy, Dement tells his students, immediately Dement is a true performer, publicly embarrassing those who fall asleep during his lecture by having one of his 10 teaching assistants spray them with squirt guns, take their pictures and ask about the last things they remember.

Dement talks about “sleep debt,” his idea that missing sleep night after night accumulates.

“Sleep debt can only be reduced by obtaining extra sleep,” he said.

Dement faults many doctors for misdiagnosing sleep-related illnesses. He gets upset when police characterize fatal car crashes caused by a driver falling asleep as “accidents without a cause.”

Each meeting, the names of students are flashed onto the screen and they are told to shout out his Hallelujah chorus, the “Red Alert” mantra. Students who don’t belt it out properly get booed by the crowd until they do it with more gusto.

“Is there any chance that in your later life you will not remember this sentence?” he asked. “The goal is to get it so etched into your mind that you don’t forget it.”

To get students excited, he used to bring narcoleptic dogs in for show-and-tell.

That unorthodox teaching style, combined with a widespread perception that the class is an easy way to fulfill the natural science general education requirement, makes him popular among students.

To spread the Good News about the benefits of sleep, Dement employs his students as disciples. One assignment is an “outreach project,” through which students relay his wisdom to the larger community.

Some traveled to Menlo-Atherton High School to give 50-minute lessons to students on dozing. Others produced videos or set up tables in White Plaza. [Disclosure: a copy of this article will be submitted as part of this reporter’s project.]

“The evidence is piling up that, as people lower their sleep debt, everything gets better from quality of life to stamina,” Dement said.

The pioneer in the scientific study of sleep is now an old-timer. He often references research he did at the University of Chicago during the 1950s — before almost all of his students’ parents were born.

Dement insists he’ll keep teaching as long as he is able, even though he temporarily stopped in 2003, after announcing it would be his last year.

He still works at least 40 hours a week and fundraises for the Sleep Disorders Clinic and Research Center that he directs. The fifth edition of his textbook for medical students is “in the works.”

He’d like to see a major or a department dedicated to the study of sleep. Dement said in an interview that Psychiatry Associate Prof. Clete Kushida might take over when he finally throws in the towel on teaching.

Personally, Dement still tries to sleep seven-and-a-half hours a night.

“I’m very, very sensitive” he said, “to being sleep deprived.”