Robert B. Parker, the best-selling mystery writer who created Spenser, a tough, glib, Boston private detective who was the hero of nearly 40 novels, died on Monday at home in Cambridge, Mass. He was 77.

The cause was a heart attack, said his agent of 37 years, Helen Brann. She said Mr. Parker had been thought to be in splendid health, and that he died at his desk, working on a book. He wrote every single day, she said.