Tonto was brought into the Lone Ranger Mythos mainly as an exposition character--someone for The Lone Ranger to verbalize the action to.
The radio series identified Tonto as a chief's son in the Potawatomi nation. For the most part, the Potawatomi did not live in the Southwestern states, and their cultural costume is different from that worn by Tonto. The choice to make Tonto a Potawatomi seems to come from Lone Ranger creator George Trendle's youth in Michigan, the traditional territory of the Potawatomi . The character might have been named after Tonto Basin, Arizona.
Here's one of the stories in that issue:
Some people, who love to judge the motives of people long dead, see Tonto as an offensive stereotype. Stereotype? Sure, we're talking comic book and 15 minute cowboy radio shows for christsakes, not a scholarly study of 19th century Native American life.
Tonto was a positive image of Indians. I don't know if there is one in pop culture today. It's a shame if there isn't.
Here are 2 more informative pages & the cover from this issue:
Tonto carried on in his own comicbook series for another 31 issues, until 1959.