Spencer Tracy was fond of telling a story about his first encounter with Katharine Hepburn. It was 1941, and the two MGM stars had tentatively agreed to co-star in a movie, "Woman of the Year." The 5-foot-7 Hepburn was wearing platform shoes that added 4 inches to her already formidable height when she met the 5-9 Tracy outside the studio commissary.

After producer Joseph L. Mankiewicz introduced them, Hepburn said, "I'm afraid I'm a little tall for you, Mr. Tracy." They shook hands, Tracy smiled, and he replied, "Don't worry, Miss Hepburn. I'll cut you down to my size."

Tracy and Hepburn fell in love while making "Woman of the Year" and remained lovers until his death, shortly after they completed their final film together, "Guess Who's Coming to Dinner," in 1967. All nine of their films have been packaged for the first time in "Tracy and Hepburn: The Definitive Collection," a 10-disc set released this week (Warner Home Video, $59.92, not rated). The collection also includes the Hepburn-narrated Emmy Award-winning documentary from 1986, "The Spencer Tracy Legacy: A Tribute by Katharine Hepburn," in which Hepburn gives her own, slightly different version of their first meeting. Two of the films, "Keeper of the Flame" (1942) and "The Sea of Grass" (1947), appearing here on DVD for the first time, are also available as single releases ($19.97 apiece).

On screen, the duo usually portrayed either a married couple or a pair of opposites who gradually attract. As a couple, they often had to go through a certain amount of conflict, even separation, before eventually working out their problems. It's the conflict and its resolution, whether played for laughs or for high drama, that remains most compelling about their screen performances.

Tracy and Hepburn never married, largely because Tracy, a Catholic, would not divorce his wife of many years, Louise, the mother of their two children and a well-respected philanthropist who founded the John Tracy Clinic for deaf children in Los Angeles. (The Tracys' son, John, was born deaf.) Tracy and Hepburn were always discrete about their relationship, and the times allowed them to maintain it without scandal or exposure.

As Hepburn biographer Anne Edwards points out, they were protected by their powerful studio, MGM, which was usually able to control press coverage of its stars, and by Louise Tracy's stature in the community, which further prevented negative gossip from appearing in print.

(These days, news of the sparks flying between Tracy and Hepburn on the set of "Woman of the Year," accompanied by smuggled cellphone videos, would have appeared the same afternoon on TMZ.)

As many film critics and historians have noted, Tracy and Hepburn are best in their comedies, whether playing an assistant district attorney who battles in court with his wife, a defense lawyer, in "Adam's Rib" (1949); a crusty boxing manager/promoter who takes on as a client an outstanding female golfer and tennis player in "Pat and Mike" (1952); or as a technocrat whose new computer may replace the work of a research librarian in "Desk Set" (1957). Hepburn's characters embody the modern, emancipated woman whose intelligence and independence is respected, even admired, by Tracy, a confident, stable yet vulnerable man. The problems in their relationship invariably occur when one of the characters crosses a line, tipping and unbalancing their 50-50 equilibrium.

"Adam's Rib," written by the couple's close friends, the husband-and-wife team of Garson Kanin and Ruth Gordon, and directed by frequent collaborator George Cukor, is the best of the Tracy-Hepburn films. (Following Tracy's death, Kanin wrote the best-selling "Tracy and Hepburn," an "intimate memoir.") As lawyers who find themselves on opposite sides of a murder case involving a distraught woman (Judy Holliday, in a star-making performance) who attempts to shoot her philandering husband (Tom Ewell), their battle of the sexes moves from the courtroom to the bedroom. The film, which seems far advanced for its time, raises some serious issues about male-female differences and the difficulty of maintaining a relationship between two career-minded people. Yet it remains a terrific comedy.

"Without Love," a shallow comedy-drama from 1945, features Tracy as a scientist and Hepburn as a widow who agree to a marriage of convenience but later discover -- surprise! -- that they really love each other.

Among the dramas, "Woman of the Year" is the best, "Keeper of the Flame" the murkiest, "Sea of Grass" the soggiest, "State of the Union" (1948) the most disappointing and "Guess Who's Coming to Dinner" the most obvious.

Hepburn portrays a character modeled after the well-known journalist Dorothy Thompson in "Woman of the Year," well-written by Ring Lardner Jr. (later a blacklisted member of the Hollywood 10) and Michael Kanin (Garson's brother) and expertly directly by George Stevens. In opposites-attract manner, she falls in love with another journalist, a sports columnist and regular guy who's not used to the international circles his new wife travels in and expects a more wifely wife. Despite an unfortunate ending tacked on by the studio heads, in which Hepburn's character can't manage the appliances of a modern kitchen, it remains a good film.

"Keeper of the Flame" doesn't live up to its potential. Released in the early days of American involvement in World War II, there's some compelling material about a popular figure who promotes "Americanism" while actually being a clandestine fascist. But the story lacks urgency or bite, despite fine performances by Hepburn as the widow of a popular, renowned businessman and Tracy as a reporter who wants to write about his life.

Elia Kazan once described directing "Sea of Grass" as his most "miserable experience" in Hollywood. The movie, about a wealthy New Mexico cattle rancher who marries a woman from the East, was actually shelved by MGM upon completion, only to be released a year later. The movie was harmed by MGM's insistence that Kazan shoot the entire film on studio sets, using stock footage of grasslands as a backdrop. In addition, Tracy and Kazan clashed over their respective styles of acting, with Tracy denigrating Kazan's "Method" acting as "a lot of high-flown mumbo-jumbo."

Director Frank Capra's "State of the Union" tries to be up-to-date politically. It's about the run-up to the 1948 presidential election and tosses in references to current issues like the anti-labor Taft-Hartley Act. But the film never gets to the heart of the political controversies of the day. Hepburn plays the estranged wife of a successful, self-made industrialist (Tracy) who is being groomed for a presidential run by two wheeler-dealers -- a ruthless newspaper publisher (Angela Lansbury, presaging her role more than a decade later in "The Manchurian Candidate"); and a conniving politician (Adolphe Menjou). In a film that doesn't ring true, the best scenes involve the cunning Lansbury and the confrontations between Hepburn's character and Menjou's. (Hepburn, like Tracy, was an ardent supporter of Franklin D. Roosevelt and the New Deal; a devout liberal, she despised the right-wing Menjou, who had testified against Hepburn before the House Un-American Activities Committee, aka HUAC, saying, "Scratch a do-gooder, like Hepburn, and they'll yell, 'Pravda.' ")

Finally, after a decade's gap between their co-starring films, Tracy and Hepburn made "Guess Who's Coming to Dinner," directed by Stanley Kramer. A box-office hit featuring an Oscar-winning performance by Hepburn, the movie is progressive in content but woodenly directed and utterly predictable. Tracy and Hepburn play a couple whose liberal views are challenged when their daughter (played by Hepburn's real-life niece, Katharine Houghton) brings home her new fiance (Sidney Poitier), a brilliant doctor who happens to be black.

Fifteen days after principal photography for "Guess Who's Coming to Dinner" was concluded, Tracy, who had been ill throughout the production, died of a heart attack. Out of deference to Louise, Hepburn did not attend Tracy's funeral.

But their love for each other is apparent in the nine movies in "Tracy and Hepburn: The Definitive Collection." It's not just acting.