Tolkien did put a lot of himself into Bombadil WarlKicken - he loved hiking in the forests and mountains in Switzerland in his youth (in fact Ransome, the hero of CS Lewis' Cosmic Trilogy, was based on Tolkien, most especially the spiritual side of him) and he also loved his baccy and beer and knew a fair bit about mushrooms too...
There was another member on here who speculated on whether he was supposed to be Tolkien or some kind of creator figure in the pantheon of Arda.
I think the Tolkien theory is the correct one in overview because there's been a lot of scholarly discussion about Tolkien in his academic life as well as the wealth of documentation and archives on Ea (the cosmos of LotR and Middle Earth which is supposedly a time/reality shift of the antediluvian Solar System and this Roundworld galaxy) that he left behind and that his son Christopher has been trying to tidy up ever since his death in the early 1970s. He's on record as saying the TB isn't
any of the Ainur - the god-angels of Ea or Eru Iluvatur their creator and All-Father of the Universe and that TB was on Arda (the whole of the Earth) before any other living being or spirit entered it... so who else could it be?
He never confirmed it one way or the other anyway, but he did base many characters in his he books on people he knew, most famously of his wife, whom he idolised, and transformed her into Luthien Tinuviel, half elf, half angel and the most beautiful being ever born on Arda (Arwen and Aragorn were both descended from her by various routes).
He sounded such a nice old chap, very thorough and attentive to detail and I think that he and Terry would likely have got on together pretty well - they certainly have the same widely read tastes and inclinations and aren't averse to bars and holding court