PHOENIX — Fritz Clapp, a 67-year-old lawyer with a bright red mohawk, practices intellectual property law. Years ago, his clients were “small-time businesses that nobody had ever heard of.” Then he found something bigger. Today, Mr. Clapp, an eloquent and irreverent man known to wear a purple fez during negotiations with other lawyers, represents the interests of a group not commonly associated with intellectual property: the Hells Angels Motorcycle Club. His main role is not as a bulldog criminal defense counsel for the notorious group but as a civilized advocate in its relentless battle to protect its many registered trademarks.

Just in the past seven years, the Hells Angels have brought more than a dozen cases in federal court, alleging infringement on apparel, jewelry, posters and yo-yos. The group has also challenged Internet domain names and a Hollywood movie — all for borrowing the motorcycle club’s name and insignias. The defendants have been large, well-known corporations like Toys “R” Us, Alexander McQueen, Amazon, Saks, Zappos, Walt Disney and Marvel Comics. And they have included a rapper’s clothing company, Dillard’s and a teenage girl who was selling embroidered patches on eBay with a design resembling the group’s “Death Head” logo.

The Hells Angels remain etched in the popular imagination as sullen, heavily muscled men in leather vests who glare from behind raised handlebars, ready to take on anyone who crosses them — rebels with no particular cause but their own form of ritualized brotherhood. But over the years, the group collectively made a leap from image to brand, becoming a recognizable marque and promoting itself on items as varied as T-shirts, coffee mugs and women’s yoga pants. Sonny Barger, 75, the longtime Hells Angels leader, at times has offered his own online bazaar of goods that bear his name: sunglasses, bottles of cabernet sauvignon and books he has written.

With more to sell and more to protect, the Hells Angels’ turn toward the litigious comes with a twist: The bikers are increasingly calling on the same legal system they deride as part of the machinery that has unfairly defined them as criminals.