LEWISVILLE, Texas — Here are a few theories as to the origin of “Mean Joe” Greene’s nickname.

There’s the story of a middle-school nemesis named “Sleepy,” who once stole the five dollars Greene’s mother had left on the television set to pay the insurance fees her son needed to play on the school’s football team.

“I popped him, knocked him down,” Greene said. “That ended it. He didn’t bother me anymore, and no one else did it. I ended up playing catch-up. I guess I caught him. So I ended up having the reputation as a bully for a while.”

There’s the reputation that girls from his hometown of Temple, Texas, brought along to North Texas in 1966, when Greene joined the football team as an imposing defensive lineman.

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“They knew me,” Greene said, “and their explanation of Joe was, ‘Oh, he’s a real nice guy, but he’s mean.’ ”

There’s the time Greene sprained his ankle during his junior season, forcing him to wear a plaster boot and tote crutches around campus. One problem: There was a big party happening, and he wanted to be free of any boot-and-crutch impediments.

Joe Greene as a college football player at North Texas. (University of North Texas)

So he went into his shower, soaked the plaster, got out of the shower, reached into a drawer, pulled out a fork — not a knife, a fork — and cut off the cast. Problem solved; party, here I come.

OK, so that doesn’t explain the birth of the nickname; it’s just an amazing story.

Of course, the name could also be born from a simple idea: Whether at North Texas, where he starred from 1966-68 on three of the best teams in school history, or with the Pittsburgh Steelers, where he put together a legendary career, Greene was always the meanest — read: most intimidating — player on the field.

But we can put one misguided theory to rest right here: The North Texas Mean Green are not, in fact, named in honor of “Mean Joe” Greene, who now lives in nearby Flower Mound, Texas, and is a fixture at North Texas home games. The extra vowel on the surname should be one giveaway, while the school’s green uniforms should be another.

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So while we’re here and on the topic, let me tell you a story about “Mean Joe” Greene, the Mean Green and how it was that North Texas swapped nicknames — the teams were once the Eagles — during Greene’s playing days in Denton.

The story begins Sept. 18, 1965, with a 65-12 loss at rival UTEP, which was then known as Texas Western University. A year later, the Miners came to Fouts Field — since replaced by Apogee Stadium — for what Greene called a “retaliation game.” It went well: North Texas won 12-9, holding UTEP to a school-record minus-44 yards rushing.

In the student section, meanwhile, basketball player Willie Davis — then, as now, one of Greene’s closet friends — began to lead a song: Go mean green, you look so good to me.

A new nickname was born.

“Willie tells me they had a little too much to drink,” Greene said.