Donald O'Connor
Donald O'Connor performed the routine in a single day on a concrete floor while smoking four packs of cigarettes a day, ended up bedridden for three days afterward — and then a car accident destroyed the original footage and he did the whole thing over again. The song was written after the shoot started, lifted almost wholesale from Cole Porter's "Be a Clown"; O'Connor built the routine from scratch on set out of 26 years of vaudeville muscle memory — the backflips, the wall-run somersault, the dive through a breakaway wall. Asked in 2003 how he pulled off the wall flips, his answer was one word: "Experience."