Hmmm... He can wrestle, is very strong, is quite proficient with a bow, rope, and spear, knows dozens of languages, can attract many followers and even has an animal companion through most of book three IIRC. He has tons of skills like climb, jump, balance, tumble, move silently, listen, hide, spot, survival (with track) maybe even escape artist. He also has the scent ability. Hmm... statting him out would be hard since his strength would have to be so high, along with intelligence, dexterity, and charisma. His wisdom and constitution can't be much lower either. He is now immortal so he not only wouldn't suffer aging effects, he will never die of natural causes. Oh, he is also quite proficient with a gun.
There are probably a lot of things that I forgot to mention since it has been many years since I read all 24 books. Anyway, it is hard for me to put him in any one or two classes. Parts of rogue, fighter, monk, druid, and ranger can all fit. Tarzan seems like he would fit much better in a custom prestige class made for him. Then I would probably use ranger/rogue to qualify for the prestige class.