In traditional palmistry, the Sun line (sometimes called the Apollo line) is a vertical crease that runs up toward the ring finger, which sits beneath the mount of Apollo — the fleshy pad associated with creativity, recognition, and a certain sunny disposition toward life. Classical palmists interpreted a strong, clear Sun line as a sign of public success, artistic talent, and the kind of charisma that makes strangers feel like they already know you.
It did not traditionally mean billionaire. It meant something closer to "this person might do rather well and people will probably like them." Which is lovely, and considerably more achievable than a nine-figure net worth.
The "billionaire line" label is a modern internet invention, almost certainly optimised for search engines and the entirely human tendency to look for good news in unusual places. It found its audience immediately, because the alternative — "the line that suggests moderate creative success and mild public recognition" — generates considerably less excitement.



