James Bowen wrote the book after meeting Bob in 2007 while battling drug addiction.
Mr. Bowen found the abandoned and injured red cat and decided to care for him.
The pair quickly became inseparable, Bob often joining Mr. Bowen as he strolled and sold The Big Issue on the streets of London.
The book on their relationship became a bestseller and was made into a 2016 movie with Luke Treadaway.
After Bob died on Monday, Bowen said, “Bob saved my life. It’s as simple as that. He gave me much more than company. With him by my side, I found a direction and a goal that I had missed.
“The success we got together through our books and movies was miraculous. He has met thousands of people, touched millions of lives. ”
He added, “There has never been a cat like him. And never will be again. I feel like the light has gone out in my life. I will never forget him. ”
Hodden & Stoughton, who published the book, said in a statement: “As James and Bob continued to find fans all over the world, Bob led an incredible life by meeting supporters during book signings, browsing the world and facing the feline celebrity.
“It was an extraordinary cat that we will miss very much. “
RIP Bob was in vogue on Twitter Tuesday evening, as many paid tribute to him.
One person said the news “really broke my heart,” while another said the cat would be “greatly missed by all.”
Bob will appear as himself in a movie sequel, A Gift from Bob, later this year.