In his telling, he is protecting put-upon inventors. But he may simply be profiteering from a flawed and creaky legal system.

Mr. Spangenberg speaks in rapid-fire clumps of words, usually while looking down and grimacing slightly, as though trying to lift a barbell. When we met, he was wearing what he calls “my uniform”: a pair of jeans and one of his 40 identical black, short-sleeve, mock-turtleneck Nike T-shirts.

He doesn’t mind his public reputation as an ogre, and by all means, he says, call him a troll — though he thinks the name is a bogus effort to taint his profession.

When it comes to work, he is focused to the point of being obsessive. As an associate at a corporate law firm — after taking the ACT test, he attended the University of Delaware and eventually earned a law degree from Case Western University — he once worked four days straight without sleep, and was taken to the hospital in an ambulance.

“I had a mild seizure,” he said. “There’s only so much coffee and caffeine tablets you can take.”

He stands about 5-foot-6 and was bullied as a child because of his height. He always fought back, he says, and he usually lost; his nose has been broken by an assortment of fists. This has given him a lifelong hatred of bullies, which explains, he says, why he wound up in a job where he often stands with a small company assailing a larger one.

But IPNav doesn’t exactly fight using the Marquess of Queensberry rules. In a 2008 ruling, Judge Barbara B. Crabb of Federal District Court in Wisconsin, concluded that Mr. Spangenberg was involved in witness tampering — specifically, inducing a lawyer to “intimidate a witness on the eve of trial.” The eviscerating 62-page ruling was in a case brought by DaimlerChrysler against a company owned by Mr. Spangenberg called Taurus IP. The carmaker accused Mr. Spangenberg of breaking a 2006 we-won’t-sue-you-again agreement over certain tech patents.

It was a complex case, but here’s a quick summary: one company controlled by Mr. Spangenberg (Orion IP) was accused of having signed a settlement with DaimlerChrysler. Later, a different Spangenberg-owned company (Taurus IP) sued DaimlerChrysler with related patents. Mr. Spangenberg seemed to be trying a double dip — angling for two settlements from the same defendant. Tsk, tsk, said Judge Crabb, though she used tougher language and painstakingly enumerated the maze of companies in the Spangenberg empire. She ordered Taurus IP to pay DaimlerChrysler $3.8 million to cover its legal fees and succinctly described Mr. Spangenberg’s business model this way: “to license patents through litigation: first file a lawsuit, then negotiate a licensing agreement as part of a settlement.”