Sources told TMZ that Mahoney's official causes of death include brain disease, lung cancer and seizures. Mahoney also reportedly suffered from kidney disease and diabetes.
The 77-year-old actor died on Sunday while in hospice care.
On Frasier, Mahoney played Martin Crane. Martin was a retired police officer who fathered both Frasier (Kelsey Grammer) and Niles Crane (David Hyde Pierce). His character suffered a gunshot wound, which lead to his retirement and moving into Frasier's home.
"He was my father. I loved him," Grammer told The Hollywood Reporter.
Among many online mourners was Modern Family casting director Jeff Greenberg. Greenberg previous served as casting director for Frasier. He shared a somber message alongside a photo of himself with the Frasier cast.
The great John Mahoney passed away today at age 77. I've not known a kinder man nor more brilliant actor. We were all blessed to have spent 11 glorious years together. pic.twitter.com/hn3SZwuEy4— Jeff Greenberg (@JeffGreenbergCD) February 5, 2018
"The great John Mahoney passed away today at age 77," Greenberg wrote. "I've not known a kinder man nor more brilliant actor. We were all blessed to have spent 11 glorious years together."
Mahoney was an acclaimed actor earning a SAG Award for Frasier and a Tony Award for portraying Artie in the play The House of Blue Leaves. He also earned Golden Globe and Emmy nominations for his Frasier role.
Mahoney was nearly 40 years old when he quit his day job as a magazine editor to pursue acting. Even before that, he taught English at Western Illinois University throughout the early 1970s.
Once he entered the world of acting, Mahoney quickly became a fixture in the Steppenwolf Theatre, a staple of the mid-western city's acting scene. After that, he took the plunge and move to New York City, where he won a Theater World Award for his work in an off-Broadway production of Orphans.
He was also known for appearing the TV Land sitcom in Hot in Cleveland, as a suitor for Elka Ostrovsky (Betty White).
He also had guest roles on Cheers, Becker, ER, Burn Notice and 3rd Rock from the Sun. In film, he had roles in Say Anything..., The American President, Reality Bites, Barton Fink and Dan in Real Life.