Donald Blake has always been a strange and complicated part of Thor's history. Created by Odin as a host for Thor while he was on Earth, the crippled young doctor had two sets of memories, and Thor unknowingly spent over a decade living in this form. A slight reboot for the character decades later led to Thor and Blake becoming two separate entities, though the doctor would lose his mind upon realising his life was a lie. He's since faded from canon, and it's for the best too as it was a confusing and weird dynamic which Marvel Studios were ultimately smart to only pay a tongue in cheek reference to rather than try to adapt.
