John David Keene was born in 1930 in Greenwich Village. Charismatic from his early years, he attended Hunter College High School and studied Political Science at Yale for 7 years.
In 1972 he was elected as a Republican Senator and in 1976 he allied himself with the New York Police Officer's Union on protesting at the liberties taken by the masked adventurers. The following year he tabled the infamous Keene Act, which banned costumed crime-fighters save those sanctioned by the government.
Louise Easton wrote an article about him.
Other than the "Keene Act", nothing else is mentioned about Keene in the original novel, not even his first name, so no identification is certain. It is possible that Senator Keene is supposed to be David Keene, Spiro Agnew's advisor during Nixon's administration.
The above persona of "John David Keene" was invented for the viral marketing surrounding the Watchmen film.