I made the following posts thinking there would only be a few of them, so I didn't try to organize them. Now that I may be done with them, I recommend reading them in this order:
On servants, sidekicks, and partners, or why I don't put Lothar, Kato, and Tonto among the first superheroes of color
Butterfly is the first black female superhero—but don't ignore Torchy Brown, Mummy Begum, Merciless, or Bubbles the Dew Dilly
More Asian and Native American public domain heroes: the Green Turtle, Fu Chang, Dr. Fung, Mantoka—plus villains!