Son of the Phantom. It's a novelization of the comic book "The Phantom" (also fairly obscure- although they did make a movie about the character, staring Billy Zane).

The book was completely unrelated to the comic book character. And honestly, it probably wasn't all that good. To ten-year-old me, it was the coolest thing ever. I sure wished I could have been the son of a costumed hero deep in the jungles of Africa, come back to America, become a hero on the football field, win the hand of the prettiest girl in school, and then move back to battle the bad guys (because it'd be my duty, of course).

I lost it decades ago to a tomcat who decided my bookcase was the best place to spray his ball musk. It's probably not nearly as good as I remember, so maybe that's not a bad thing.