There are any number of quotes from King Lear that one might employ to kick off a discussion of how fully Glenda Jackson embodies William Shakespeare's disintegrating ruler. 'Every inch a King,' might do, though it is spoken ironically in Act IV, when things have fallen well apart. Rather, what came to mind not long into a viewing of director Sam Gold's outstanding production of Lear now at New York's Cort Theatre, was the bit of dialogue above, from Terrence McNally's 1994 play Love! Valour! Compassion!. Machismo just begins to graze it. The tragedy of the mad king is a study of masculine power battling its own decline and Jackson, with self-ruinous male ego animating her wiry frame, feasts on the notoriously challenging role.