Robert Stevenson

Because the clashing powers of Walt Disney and P.L. Travers is the most infamous and soap opera-worthy aspect of the filming of Mary Poppins, we sometimes forget about its low-key director. He might seem like the Ringo of the group—you know, quiet, inauspicious, and untalented in comparison.

But don't dismiss him. (Don't dismiss Ringo, either—dude wrote "Octopus's Garden.")

Stevenson was actually an extremely prolific director, taking the helm on tons of Disney live-action classics, like Old Yeller, The Absent-Minded Professor, Bedknobs and Broomsticks, and Chitty Chitty Bang Bang. He was Disney's go-to live-action guy. (Source)

Stevenson was British, and cut his teeth as a filmmaker by helping film the liberation of Rome sequence in Frank Capra's famous Why We Fight propaganda films, which were designed to bolster the Allied cause in World War II. So we can add "helped beat Hitler and Mussolini" to the Stevenson resume.

Also, before becoming the Big Kahuna of Disney live-action, Stevenson got involved in television, and went on to oversee about a hundred TV productions. (Source)

No, Stevenson didn't go in for moody, impressionistic noir films or abstract homages to Big Ideas—instead, his movies are all about having a family-friendly good time. But Mary Poppins did manage to secure Stevenson an Oscar nomination—so it's not like no one acknowledged his artistic talent.

Plus, he'd already helped fight the Nazis with Capra's film. And once you've helped to beat Hitler, the ultimate bad guy, there's no shame in taking it easy and directing things like The Love Bug and That Darn Cat! (Source)