Ben Stiller, Jack Black, Robert Downey Jr., Matthew McConaughey and Tom Cruise. Tropic Thunder is peppered with actors who’ve padded the coffers at Paramount Pictures, the studio that’s releasing this comedy as part of its DreamWorks acquisition. And after this subversive romp, consider their collective $4,970,802,499 at the box office as long-held escrow on a legendary prank.

If biting satire as exuberantly insane as it is intelligent could be considered the stuff of sequels, call Tropic Thunder a follow-up to Zoolander (both of which Stiller also co-wrote and directed).

The modern Hollywood star-system, Oscar-pandering actors, studio-executive ogres, whacked-out method performances, war-hero opportunists, action-film expectations, ghetto culture as a commodity — each is mocked with brilliant buffoonery. And what’s not sent up in this film within a film is blown up … and good. Thunder is as exciting as the many shoot-’em-ups in its target sights.

And even before Thunder rolls, it’s 2008’s funniest comedy. Be sure to arrive early for its uproarious parodies of trailers and commercials, complete with real studio logos, and the best riff on commercialized black culture since Fear of a Black Hat.

Stiller, Black and Downey Jr. are actors in a film called Tropic Thunder, based on the memoirs of Four Leaf Tayback (Nick Nolte), a Vietnam veteran who returned home with hooks for hands.

After five days, the film is “100 days behind schedule” thanks to inept, inexperienced director Damien Cockburn (Steve Coogan). Meanwhile, Tayback’s actual heroism matters little to the leads beyond how they can exploit it for their careers.

For fading star Tugg Speedman (Stiller), playing Tayback has potential to bait Oscar and rebound from both a limp adventure franchise (Scorcher VI: Global Meltdown) and a bad-idea role as a mentally handicapped farmhand in Simple Jack (a role that later will truly haunt Tugg).

As a flipside to vapid male model Derek Zoolander, Stiller plays Tugg as a comic straight man reacting to the craziness around him (excepting one hilarious gone-native moment). While not totally believable even as a fake action hero, Stiller sells the lead well enough to function.

Comic Jeff Portnoy (Black) has a chance to … well, score pure heroin on location in Myanmar. To start, Black gives the least-impressive lead performance. But his capacity for crazed humor grows with Jeff’s jones for drugs, culminating in a filthy, but appropriately desperate, monologue.

Blue-eyed, lily-white Aussie Kirk Lazarus (Downey Jr.) sees Sgt. Lincoln Osiris as the ultimate transformation — surgically altering his skin to play a man who happens to be black.

Resembling Cleavon Little possessed by the devil, the wily Downey is smart enough to know this isn’t a role that’s racially offensive. It’s a satirically inspired channeling of the great Peter Sellers, and, at the right moment, it’s emotionally convincing as a declaration of dedication.

Downey cloaks Kirk in so many rabbit-hole layers of character that you fear he won’t resurrect the real him. (At one point, Kirk adopts a Myanmar accent filtered through black patois strained through Aussie speech patterns. It’s mind-bogglingly outrageous.)

At the end of his rope and through Tayback’s urging, Damien goes guerilla, shooting alone with actors on cameras deep in the jungle far from Tugg, Kirk and Jeff’s trailers.

Things turn deadly when drug dealers violently ambush the cast and crew, kill some, kidnap others and leave those left standing armed only with their acting as ammo to get out alive.

Meanwhile, back home, Tugg’s aim-to-please agent Rick “Pecker” Peck (McConaughey) butts heads with Les Grossman — a fat, bald, foul-mouthed, hairy-knuckled studio chief who chugs diet soda, cranks Flo Rida and only sees the upside in leaving his actors thrown to the wolves. It takes a moment to sink in that it’s Cruise under the flab, hairpiece and sweaty misanthropy. Once it does, it’s clear it’s his best work since the last time he shocked us (Magnolia).

Cruise is wisely credited, as the role is so much more than a cameo — it’s the actor’s brave, crazy stare-down of his current career crisis, of which Cruise’s well-publicized Paramount acrimony is a part. It’s the same freeing break from monotony John Travolta found in a fatsuit for Hairspray, and Cruise walks away from this re-christened in cool … at least until the next Scientology rant.

Tropic Thunder plays like a party with punch spiked not with vodka but six sheets of acid. The result is a story more wildly unpredictable than anything any of its actors have done in years. All at once, it gloriously deconstructs actors’ insecurities, kicks butt as a kitchen-sink action film and surprises us with unhinged gory comedy. And unlike Pineapple Express, it’s even crazier and funnier as it soldiers on, particularly trudging into the neuroses of its supporting players.

Those offering such able assistance are: Jay Baruchel as Kevin Sandusky, a no-name actor; Brandon T. Jackson as Alpa Chino (say it fast), a black rapper who culturally butts heads with Kirk’s approach; and the great Danny McBride as Cody, a staged demolitions expert with lightning bolts shaved into his sideburns.

Everyone involved doesn’t just flip the bird here. They turn it on its side, wrap it in tinsel and twirl it around. It’s off-their-rocker romping and comedy gold in one of the year’s best films.