The 20th season of American Masters on PBS kicks off with the premiere of two new films: “John Ford/John Wayne: The Filmmaker and The Legend” (tonight at 9 p.m.) and “The World of Nat King Cole” (May 17 at 9 p.m).

The celebrated documentary series has always strived to situate its subjects within the broader American experience, to make them somehow emblematic of their culture and times. In this respect, John Ford and John Wayne are ideal subjects.Their work and lives played out against the backdrop of the most enduring of American film genres, the Western. Ford would perfect its visual language, deepening and complicating its message; Wayne would become its most memorable and bankable star. But though they worked on 14 films together, they came to represent very different ideas about how the Western, and America, should be understood.

The partnership between the two – among the most celebrated in American film – almost ended before it began. As the most successful director of his day, Ford related to his employees as a god – all-powerful and vengeful. Cast and crew alike called him “pappy” on set, and bent to his every whim.

Wayne entered Ford’s world as a stagehand, working just off camera. With his gruff good looks and instinctive masculinity, it was perhaps inevitable that he would someday enter its frame. But Ford brought him along slowly, giving him only bit parts. And when Wayne took a leading part in Raoul Walsh’s 1930 film “The Big Trail,” Ford excommunicated him. The film was a flop, and Wayne was relegated to C-movie roles.

Ford finally brought him back into the fold to star as the Ringo Kid in the 1939 film “Stagecoach,” a part which set the pattern for Wayne as Ford’s – and America’s – favorite good-bad man. “Wayne was to Ford what David was to Michelangelo,” observes one of the film’s commentators, “the ideal man.”

Ford spent the war years making propaganda films for the Navy and was on hand to shoot footage of the battles of Midway and Normandy. Wayne, meanwhile, opted out of military service (much to Ford’s annoyance), choosing instead to play the war hero on the big screen.

The two would come together after the war to work on a series of films that punctured the very nationalistic myths Ford had helped create a few years before.”They Were Expendable” and “She Wore A Yellow Ribbon” displayed Ford’s growing unease about the rituals, pride, and pageantry that made young men so willing to die for their countries.

Off-screen the two couldn’t have disagreed more. Even as Ford was inveighing against loyalty oaths in the Director’s Guild, Wayne was emerging as one of the most prominent members of the Motion Picture Alliance and spearheaded the Hollywood blacklist.

“The World of Nat King Cole” strains to manufacture such social significance. Born in Montgomery, Alabama in 1919, Cole’s family was part of the Great Migration that took millions of blacks from the agrarian (and race-in flamed) South to the industrial North.

Cole ended up in Chicago, where he was exposed to the bustling jazz scene of the day. He saw Duke Ellington live. He was close enough to the Terrace Ballroom that when his family’s radio tube blew out during the broadcast of an Earl Hines concert, he was able to rush to the club to hear the conclusion of the set. He became something of a musical prodigy himself, playing downtown nightclubs and appearing in the Chicago Defender before he graduated high school.

Cole was exempted from military service because of his flat feet, but the film nonetheless tries to find a place for him in the events of World War II, claiming his pithy 1944 hit “Straighten Up and Fly Right” was an anthem that united the country.The filmmakers are on firmer footing presenting Cole as a pioneering black artist. He was among the first to sell to white audiences right alongside – and in equal number to – singers like Frank Sinatra and Peggy Lee. Never outspoken about matters of race, he still came to symbolize the emerging black middle class, making a degree of friction with an increasingly anxious white society inevitable.

The film tells us that Cole and his family were harassed and that he was once attacked on stage, but Cole faced all of this with characteristic reserve and grace.When sponsors failed to step up to support his popular television show, the first hosted by an African American, he said only, “Madison Avenue’s afraid of the dark.”

But going off the air marked the start of Cole’s popular decline. He was unwilling or unable to change with the times. (There’s great footage of him singing the lines, “I got news sir, Nathaniel must refuse you / Mr. Cole won’t rock ‘n’ roll.”)

The film sputters to a close as it tracks Cole’s final years spent courting an international audience. (He rerecorded his hit songs in Spanish, German, and Japanese.) Which points up one of the weakness of the American Masters series: when America loses interest in the subjects, so do the filmmakers of American Masters.