Mark Fischer, who knew nearly all there was to know about copyright and entertainment law, used his law firm blog to reach beyond his immediate clients, writing eloquently and drolly about questions that arise at the legal crossroads where celebrity, social media, and the Internet collide.

"He really carved himself out an international reputation on new media and its protections," said John Taylor "Ike" Williams of the firm Sennott & Williams, a longtime friend who worked closely with Mr. Fischer for 25 years at previous firms.

Want to know if you can be sued for posting a scathing restaurant review on Yelp? Mr. Fischer offered guidance. Wading into disputes that might seem absurd or arcane to the untrained eye, he skipped nimbly from insight to bemusement while discussing the unauthorized use of singer Rihanna’s face on a T-shirt, whether a deejay can copyright a playlist, and a $6 million lawsuit over a tweet with a photo of actress Katherine Heigl carrying a pharmacy shopping bag.

He also offered thoughts about the famous selfies shot by a black macaque monkey in Indonesia that used a camera owned by David Slater, a wildlife photographer. Slater argued that because he owned and set up the camera, he also owned the monkey’s selfies. “Animal-created copyrighted works” present a legal quandary, Mr. Fischer wrote in a blog post that became a hit on the Internet. "My labradoodle, Madison, is talented in many ways. But I know her well enough to say with accuracy that she would much rather have a strip of bacon than a copyright. Even in recognition of the growing trend of animal rights, it may be best to keep animals and copyright lawyers apart when it comes to legal issues."

A partner in the Boston offices of the law firm Duane Morris, Mr. Fischer was known as a rock star mentor to aspiring attorneys and aspiring rock stars alike. He died Wednesday in Massachusetts General Hospital of complications from organ transplants.

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