First and foremost, there's Collins the "half-breed scout." He leads the Texas Rangers into a canyon after the Cavendish gang. But it's an ambush; Collins is working for Cavendish. The outlaws fire until all the Rangers are apparently dead. Cavendish then shoot Collins because anyone who would betray people is someone who can't be trusted.
I think people in the Old West considered "half-breeds" to be more Indian than white. Whatever the case, it's clear everyone thinks Collins is the lowest form of scum. Other than Tonto, he's the only character "tainted" by Indian blood. Like "half-breeds" throughout fictional history, being part Indian has made him corrupt and evil.
Why make Collins a "half-breed"? He looks Anglo, so that can't be it. He plays no role except a one-dimensional villain in the story. So why not make him a white man?
Because it let the creators have it both ways. No genuine white man would betray the Texas Rangers or the future Lone Ranger. But blaming this treachery on an Indian would be racist and stereotypical. So the creators found another category of humanity to blame. Since mixed-race people didn't have many defenders, Hollywood could malign them with impunity.
Soon we learn that "renegade" Indians destroyed Tonto's village and killed his mother and sisters. Young Tonto was the only one left alive--the only one we see. The smoking ruins attest to the Indians' cruelty.
Message to viewers: Full-blooded Indians are murderous savages. Half-blooded Indians are traitorous cowards. Tonto is the exception that proves the rule: that most Indians are bad.
Tonto would have to be a paragon of virtue to make up for this message. Alas, he isn't. He's about as positive a character as Stepin Fetchit.
Tonto the Apache
Tonto is never called anything but an "Indian," but some clues suggest he's Apache:
But in Enter the Lone Ranger, Tonto is a generic Indian, not an Apache. He's dressed in generic buckskins and wears a generic headband. He talks and acts like a generic Indian.
As we'll see, being generic is the least of his problems.
For more on the subject, see The Lone Ranger.