I like to make up my own theories.
R/B/Y: HE WERSSELED A ONYX IN TO SUBMISSION, AS HE HAD NO NEED FOR POKEBALLS. WITH HIS ONYX, HE FORGED A PATH THROUGH VIRIDIAN FOREST, CHEWED THROUGH MT.MOON, AND CREATED THE ROCK TUNNEL. TO TAKE A BREAK, HE DEFEATED ALL OF THE GYMLEADERS. HE THEN DUG A HOLE THROUGH WHAT IS NOW CALLED VICTORY ROAD, WITH HIS BEARD. TO TAKE A BREAK, HE DEFEATED THE ELITE FOUR. FINALLY, HE PASSED ON HIS LEGACY WITH A KANTO WOMAN OF PALLETE. HIS FINAL TASK WAS TO RESIDE ON MT SILVER FOR ALL TIME, UNTILL HE WAS SURPASSED BY HIS SON. HIS CURRENT WHEREABOUTS ARE UNKNOWN.
G/S/C: BORN OF THUNDER AND LIGHTING, HE BUILT TOJO FALLS, WITH HS BARE HANDS. WITH THOSE MIGHTY HANDS, HE DEFEATED AN URSARING, BY ARM WRESTELING IT. HE TOO HAD NO NEED FOR POKEBALLS. WITH HIS MIGHTY URSARING AT HIS SIDE, HE FOARGED A PATH THROUGH UNION CAVE, ILEX FOREST MT.MORTAR, AND ICE PATH. HE THEN WERESTELED A RED GYARADOS IN TO SUBMISSION. HE DEFEATED ALL OF THE JHOTO GYMLEADERS, EXCEPT FOR CLAIR, WHO SURRENDERED THE RISINGBADGE WITHOUT QUESTION. HE CLIMBED OVER VICTORY ROAD, WITH POKEMON ON HIS BACK, AND NO ROPE. HE THEN TOOK OUT THE ELITE FOUR. HIS FINAL TASK WAS TO PASS ON HIS LEGACY, WITH A WOMAN OF NEWBARK TOWN. HIS CURRENT WHEREABOUTS ARE UNKNOWN.
Fr/Lg/Hg/Ss are the same thing.
Why we never heard of them:
They were highly regarded as legend, and dismissed just as easily. They never gave a name to anbody who asked, instead offering a blazing, soul piercing stare. No two people were able to agree on what he looks like. Because of this, over time people simply forgot about him.