Mr. Kramer, who graduated from Yale Law School in 1953, helped start the firm after finding that opportunities for Jewish lawyers, even those who were Ivy League educated, were limited at large firms. Early on, the firm set a nontraditional course, bringing in a psychiatrist to help lawyers deal with stress and encouraging associate lawyers to write annual critiques of partners, a practice that participants described as often brutal, but therapeutic. Outside legal circles, Mr. Kramer was perhaps best known as the inspiration for the character of Ben Weeks in “The Normal Heart,” the autobiographical 1985 play by his younger brother, Larry, which used the theater to bring attention to the AIDS crisis. In the play, Ben is painfully ambivalent about his brother’s homosexuality. In real life, Arthur ultimately came to accept Larry as a gay man, a reconciliation that was the subject of a front-page article in The New York Times in 2006. Arthur Kramer gave Yale University a $1 million grant in 2001 to create the Larry Kramer Initiative for Lesbian and Gay Studies. His influence led his law firm to become active, on a pro bono basis, in causes like marriage rights for gay couples. Besides his brother, of Manhattan, Mr. Kramer is survived by his wife, Alice; their children, Liza, of Berkeley, Calif.; Rebecca, of Manhattan; and Andrew, of Sands Point, N.Y.; another daughter, Andrea McNicol, of Manhattan; and four grandchildren.