Each time I've watched Nathan Lane in The Nance over the past five months, I have observed the actor not just as his character, Chauncey Miles, but Chauncey Miles as seen through the prism of Lane's other roles: 18 previous shows on Broadway, all of which I saw, and countless productions off-Broadway, many of which I caught. When I watch Chauncey in the witness box, for example, appearing before a judge on April 17, 1937, I am also seeing Lane during the court scene in his most popular Broadway role, in The Producers. The way Chauncey says "Who even knew there were Lutherans in New York City?" carries the absurdist smack of Max Bialystock. 

Yet when, a moment later, Chauncey makes his principled stand against censorship - "All we do at the Irving Place is get the audience to laugh. Laugh at - the gap between what is known and what can be said" - I think not of Max but the persecuted screenwriter Dalton Trumbo, who Lane played off-Broadway in 2003 in Trumbo: Red, White and Blacklisted. Socialist-hating Chauncey would, I suspect, object to the association strenuously. 

On Broadway, Lane has appeared mostly in comedies and musicals, so I can imagine some theatergoers being rather surprised by his scenes of achingly realistic decline in The Nance. From Guys and Dolls to A Funny Thing Happened on the Way to the Forum, from Wind in the Willows to The Addams Family, Lane has sung and danced his way into the roster of musical-comedy greats suitable for family consumption, so to watch Chauncey arrive home drunk and confess to a lover his public-park promiscuity may be a surprise for a Midwestern Lutheran tourist out for a pleasant time. 

But the truth is that Lane, all along during the past thirty years, has been conducting a parallel career as a first-rate dramatic actor, in roles that not only please but challenge an audience. He just hasn't received quite as much attention for it. I remember how startled I was, as the curtain went up on a 1988 production of Jon Robin Baitz's The Film Society, to realize that the actor playing one of the serious teachers at a South African prep school was the same performer I had seen do the frothy Roland Maule in George C. Scott's 1982 production of Noel Coward's Present Laughter, which was Lane's Broadway debut. It has been Lane's good fortune to develop a public which did not resent him, a great comedian, for turning serious. This isn't a given: while audiences generally applaud an actor established in drama for letting his hair down in comedy, they often resent a comedian for turning serious. If you don't believe me, ask Jim Carrey. 

Watching Lane in The Nance, I am aware of not just how he conjures our memories of him in other roles, but of how he, consciously or unconsciously, reminds us of other great comic performers. During the hotel-farce sketch, for instance, Lane holds his hand under his chin and turns his face, in pure Jack Benny fashion. When he turns his leg in the cast-party scene at his apartment, just before he joins other in impromptu dancing, he is channeling Jackie Gleason: Lane has named the Honeymooner as an artistic inspiration and, a decade ago, almost played him in a movie biopic. As for his work ethic, Lane has the stamina of Ethel Merman, or, to choose a fictional example, ofAll About Eve's Broadway star Margo Channing, of whom Karen Richards (Celeste Holm) says, "If she can walk, she plays." To wit: Lane injured his ankle during a "Nance" performance last month. The next morning, he went to physical therapy; the next night, he went on. 

Big-screen audiences also know Lane best for his comedy work - the 1996 hit,The Birdcage, and small-screen audiences have seen light programs such as Disney's "Timon and Pumbaa" and "Teacher's Pet," both of which won for the actor Daytime Emmy Awards. So associated is he with comedy, in fact, that a friend of mine, who rarely attends the theater, told me how surprised she was to see Lane last season on TV's "The Good Wife." "He was entirely serious," she said, "and there was no schtick." "Honey," I replied, "you haven't been paying attention." 

Lane just received two new Emmy nominations, for his serious performance on "The Good Wife," and for his loud-fashion silly billy, Pepper Saltzman, on "Modern Family." This cements for the mass audience what New York theatergoers have known all along: Lane wears both masks of Janus with authority. I would still contend, however, that never has Lane worn both in the same role as brilliantly as as he does in The Nance. 

Brendan Lemon is the American theater critic for the Financial Times and the editor of lemonwade.com