A year after that, he collaborated with the rapper B.o.B. on the hit "Nothin' on You," and co-wrote Travis McCoy's "Billionaire." Both titles were Top 10 hits. Mars was just 24 years old.

It likely wasn’t the first time Bruno Mars played his song “Billionaire” in front of an actual billionaire. But as the pop-soul hitmaker sang about wanting to “buy all of the things I ...