While this is not the case with every actor and director, one can say that for every great actor, there's often a great director who mentored him to a successful film career, and for many great directors, there's that one reliable actor they go to again and again to get their material across.
1. Elia Kazan/Marlon Brando-All of the actors of today look up to DeNiro, Hoffman, Hackman, Duvall and Pacino and those actors all idolized Brando. Brando learned his craft at the actor's studio which was co-founded by Kazan and it was Kazan who discovered Brando on stage and fought for him to be cast into Streetcar Named Desire, which along with On the Waterfront became two of the best performances ever captured onscreen. With so many aspiring actors cutting their teeth on screenplays from the Kazan/Brando collaborations, it's hard to argue any other way.
2. John Ford/John Wayne-It's not just remarkable how much Ford and Wayne contributed to the Western, but how much they grew with the Western and evolved with the genre. Normally, with a genre, you have one director who accomplishes something big, and then the genre moves in a different direction as another filmmaker comes. Ford and Wayne didn't just create the preeminent Westerns of their day, but they evolved along with the genre. There's significant difference in John Wayne's stock character between Stagecoach and The Searcher with a lot of variation in between. They also ventured outside the Western for the Irish period piece, Quiet Man, which one John Ford an Oscar. Of their 22 films together, other highlights include She Wore a Yellow Ribbon, How the West Was Won, Rio Grande and Man Who Shot Liberty Valance.
3. Frank Capra/Jimmy Stewart-Frank Capra was the 1930's version of Spielberg and Scorsesee roled into one. He was the most respected, revered and commercially successful director of his time. His visions of homespun Americana gave hope to millions during the Great Depression. His two primary collaborators were Gary Cooper and Jimmy Stewart, and while I appreciate the Cooper/Capra pairings, I don't think anyone epitomized Capra's vision nearly as well as the wide-eyed Midwestern, Jimmy Stewart. Two of Capra's three entries onto AFI's 100 Greatest Films list, Mr. Smith Goes to Washington and It's a Wonderful Life, featured Stewart front and center. In addition, James Stewart starred in You Can't Take it With You which won Capra his second best picture Oscar.
4. Martin Scorsese/Robert DeNiro-Under Scorsese DeNiro hasn played a musician (New York, New York), a sexual predator (Cape Fear), a depressed taxi driver (Taxi Driver), a boxer (Raging Bull) and more. Scorsese used De Niro at every possible opportunity. The only major films Scorsese left DeNiro out of the lead part in the 20th century were Alice Doesn't Live Here Anymore (a family melodrama centered around a female lead), The Color of Money (which couldn't have called itself a sequel if it didn't use Paul Newman, and Last Temptation of Christ (which used Willem Dafoe instead).
5. John Huston/Humphrey Bogart-The stories behind the films alone, of the two going drinking off in the primitive jungles of Africa, are worth hearing about. Huston's three most prominent films, Maltese Falcon, African Queen, and Treasure of Sierra Madre all feature Bogart in addition to the parody Beat the Devil. Huston also won Bogie his only Oscar in The African Queen.
6. Billy Wilder/Jack Lemmon-Wilder worked for 20 years before finding the perfect comic muse in Lemmon. Lemmon embraced cross-dressing in Some Like it Hot, the plight of the working class in The Apartment, and had five other memorable collaborations with Wilder. It was through Wilder, that Lemmon also got introduced to his other half (comedically speaking): Walter Matthau. Lemmon and Wilder tended to veer for the comic, but in Avanti! and Apartment, they approached dramatic elements as well.
7. Martin Scorsese/Leonardo DiCaprio-Leo DiCaprio has grown so much in the three Scorsese collaborations from Gangs of New York to The Aviator to The Departed, it's amazing. In Gangs of New York he was just a capable actor with movie star looks, by Departed he was the preeminent actor of his generation.
8. Vincente Minelli/Judy Garland-Judy Garland was MGM's preeminent child star and most valuable commodity, but as she aged, the studio needed a movie made that would move her out of her teenage roles. Vincente Minelli, originally an art director, came along and had his biggest film to date, Meet me in St. Louis, that also introduced Judy Garland, as a full-fledged adult. They also got married (a union that didn't end particularly well due to her addiction to painkillers) and produced (for better or worse) future musical star Liza Minelli. They did make four other films together including "The Pirate."
9. George Lucas/Harrison Ford-If you don't count sequels, Lucas has had a sum total of 4 creative ventures which he has unleashed on the world and Harrison Ford was a part of three of them. Lucas discovered Ford in his 2nd film, and Ford returned the favor by turning his two main creative ventures, the Star Wars and Indiana Jones trilogies into massive successes.
10. David Lean/Alec Guiness-Erase the filmographies of David Lean and Alec Guiness and there's very little reason at all to celebrate British cinema as a seperate genre. The two worked together on six films and while Guiness wasn't the star in all of them, he played a part in all of Lean's greatest successes (with the exception of Brief Encounter). The highlight, of course, was the Oscar-winning film Bridge on the River Kwai, which brought Oscars to both Lean and Guiness.
11. Stanley Donen/Gene Kelly-Kelly was also the co-director but they took over as MGM's most prominent team and worked their way up the ranks at MGM as a directing team. At first they took over Busby Berkley's troubled production of Take Me Out to the Ballgame before scoring a homerun in On the Town. In 1952, they followed that up with the most memorable film of the MGM musical era with Singing in the Rain. Donen then had a sole directing credit with Kelly as the star for It's Always Fair Weather, and after that Donen went on to become a prominent director in his own right.
12. Sidney Lumet/Sean Connery-Connery's best films outside of Bond were with Lumet and that's the director where he learned to be a serious actor from. Their most memorable collaborations were The Hill and Murder on the Orient Express.
13. Howard Hawks/Cary Grant-Grant was the early prototype of an action star. He was known as a suave matinee idol who could be molded to play the lead in any romantic film. For his own part, Grant saw himself as a funnyman who enjoyed playing around with good dialogue and Hawks supplied that in abundance. Grant has his most memorable performances when he's able to show off his flair for good comic timing and Bringing Up Baby, Only Angels have Wings, and His Girl Friday showcase his finest moments.
14. Tim Burton/Jonny Depp-Jonny Depp had been in five movies including the Oscar-winner Platoon before breaking out in Tim Burton's Edward Scissorhands. Although he only spoke 169 words of dialogue, Depp found his niche in off-beat behavior and Burton found a star that embraced his dark Gothic visions. The two have since worked together in Ed Wood, Sleepy Hollow, Corpse Bride, Charlie and the Chocolate Factory, Sweeny Todd and have two more collaborations slated for 2010 and 2011, according to imdb.
15. Billy Wilder/Marilyn Monroe-Without him, she was barely capable of memorizing her lines in order, and it wasn't lost on Billy Wilder that his Aunt Mitzy could act better than Marilyn Monroe. "Then again," reasoned Wilder, "No one wants to pay to see my Aunt Mitzy." So Wilder learned to work with Monroe's weaknesses and the end result were two of his finest films in Some Like it Hot and Seven Year Itch. Marilyn Monroe was beautiful for sure, but Wilder made her look witty, alluring, and by all measures, a movie star.
16. Stanley Kramer/Spencer Tracy-Tracy provided "It's a Mad, Mad, Mad, Mad, Mad World" with a necessary counterweight. Amid all the comics running around, Stanley's character (a disheveled cop who flirts with the possibility of abandoning his post to chase after buried loot), was the one character with pathos. In three other films with Kramer, Guess Who's Coming to Dinner, Judgment at Nuremberg, and Inherit the Wind, Spencer Tracy turned out his best work.
17. Ethan Coen & Joel Coen/Frances McDormand-The Coen brothers have elevated the careers of bit players like John Turturro, John Goodman, William H. Macy, and Steve Buscemi. They have also provided memorable turns for leading men such as Nicholas Cage, Jeff Bridges, Tom Hanks, Billy Bob Thorton and George Clooney. Let's not forget, however, that they let women join in the fun as well. In particular, Frances McDormand has been able to shine in one of the meatiest comic roles of the decade in Fargo. In addition, she's featured prominently in Burn After Reading, Man Who Wasn't There and had a small cameo in Barton Fink.
18. Stephen Soderbergh/George Clooney-Soderbergh gave Clooney his big break in Out of Sight and even after that bombed, the two kept working together in Ocean's 11 and pretty much everything else. The two have experimented together with the HBO's "K Street", Solaris, and The Good German and are often producing partners. Soderbergh's influence on Clooney is pretty well-documented and when Clooeny's not starring directly for Soderbergh, he could be starring alongside Soderbergh staples like Brad Pitt or with Stephen Gaughan who wrote the Oscar-winning screenplay for Soderbergh's Traffic. A few negative points go to Soderbergh for all the alleged fooling around on the set of Ocean's 12 that Soderbergh and crew distracted themselves with.
19. Sydney Pollack/Robert Redford-Pollack and Redford were good friends and collaborators who shared socially-conscious attitudes towards filmmaking. Without Redford, one might reconsider just how far into the political realm Pollack might have gone in the first place. Redford and Pollack's collaboration in Out of Africa led to an Oscar for the film. As Pollack's recent funeral was an indicator, Redford considered Pollack one of his greatest friends and mentors.
20. Orson Welles/Joseph Cotten-Cotten was Welles' old chum at the Mercury Theater and put him in Magnificent Ambersons, Citizen Kane, and Touch of Evil. Wells and Cotten's best performances were in the British thriller The Third Man co-starring alongside each other, but it must be noted, it was directed by a third party.