I agree with pecooper. ERB's books have lasted way longer than might have been expected. Princess of Mars is now over 100 years old; and, however good, this is still genre literature and has had much greater staying power than most such.

There are not more than a tiny handful of characters that have reached the iconic status of Tarzan in their cultures.

Everybody in the English-speaking world and many beyond still know who Tarzan is.