All SuperHeroes and Villains data from all universes under a single API.
SuperHeroes API is a free Games & Comics API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Details from superheroapi.com.

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Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
The SuperHeroes API is provided by SuperHero API (superheroapi.com).
Yes. The SuperHeroes API is listed in the Games & Comics category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The SuperHeroes API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the SuperHeroes API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The SuperHeroes API is served over HTTPS, so it's safe to use in production.