paladin

paladin \PAL-uh-din\, noun:

1. A knight-errant; a distinguished champion of a medieval king or prince; as, the paladins of Charlemagne.
2. A champion of a cause.

Once in power, though, Clinton stumbled repeatedly over obstacles created by the schizoid campaign he had conducted, in which he had cast himself simultaneously as the champion of a more conservative Democratic credo and as a paladin of the party's traditional activism.
-- Robert Shogan, The Fate of the Union

Even Columbia University economist Jagdisch Baghwati, the paladin of free trade, calls for controls on capital flow.
-- "Terrors in the Sun", The Nation, June 29, 1998

Matisse, paladin of modernism, is a long way from us now.
-- Robert Hughes, "The Color of Genius", Time, September 28, 1992

. . .the celebrated but distrusted paladin of imperialism and the romantic conception of life, the swashbuckling militarist, the vehement orator and journalist, the most public of public personalities in a world dedicated to the cultivation of private virtues, the Chancellor of the Exchequer of the Conservative Government then in power, Mr. Winston Churchill.
-- Isaiah Berlin, "Mr. Churchill", The Atlantic, September 1949

Paladin derives from Late Latin palatinus, "an officer of the palace," from Latin palatium, "royal residence, palace," from Palatium, one of the seven hills of Rome, on which Augustus had his residence.