“Emperor” starts slowly and peters out from there. Rather than a grand historical drama of the old school, it’s an unimaginative, shallow parade of artificial film moments. Cardboard characterizations and mostly lackluster casting prevent the film from being in any way memorable.

In 1945 Gen. Douglas MacArthur juggles the political concerns attending the occupation of Japan. As Supreme Commander of the Allied Powers, he was tasked with overseeing Japan’s disarmament, liberalization and democratization. Engineering vast social change while respecting the nation’s feudal traditions would be challenge enough, but MacArthur had an additional assignment. He was to recommend whether Emperor Hirohito should be deposed and tried for war crimes. The emperor was revered as a deity by his people, and there was real danger that a trial would ignite a bloody uprising.

The film’s trump card is casting Tommy Lee Jones to play the obstinate, brilliant glory hound MacArthur. If he were the focus of the drama, this would be his film from start to finish. Inexplicably, “Emperor” pushes its most compelling character into the wings to focus on one of MacArthur’s assistants and his romantic travails. Matthew Fox plays Gen. Bonner Fellers, the Americans’ top Japan expert and point man on the inquiry into Hirohito’s culpability. He’s starchy, too noble and a doe-eyed sap mooning in secret over his long-lost Japanese love Aya (Eriko Hatsune). This is the kind of movie that spells out characters’ motivations in the shallowest possible terms.

In a pitiably rickety framing story, we’re informed that Fellers and Aya had a love affair years earlier when she was an exchange student at his university. Seeing Fox, who is 46, play an ardent young Joe College in flashbacks is a dire experience. As he searches the ruins of Japan years later for the vanished Aya, you get tired of the closeups of his distraught face as he suffers nobly.

Fox’s performance is to Jones’ too-brief star turn what a wilted parsley garnish is to a big, sizzling steak. Jones revels in the general’s flair for dramatics, his photo-savvy use of khaki garb, aviator sunglasses and jaunty corncob pipe. He nails the man’s swaggering sense of himself as a giant historical figure, foreshadowing the grandiosity that provoked President Harry Truman to fire him. Yet Jones is trapped in the stilted, witless story.

In one way, though, this movie is worthy of note. Following “Speed Racer” and “Alex Cross,” “Emperor” pushes Fox ahead in his race with Nicolas Cage and Robert Pattinson for who can leave the worst acting legacy.