First appearance = Captain Marvel Adventures #22 (March 26, 1943) from Fawcett Comics.
Mr. Mind was featured in the serialized story "The Monster Society of Evil" which took place over 25 issues.
(NOTE: The chapters of the story were only a portion of the comic book. There were other Captain Marvel stories as well in each issue.)
Also, in his first few appearances, neither Captain Marvel nor the readers ever saw "Mr. Mind".
He was just a voice that was broadcasting, and others did his work for him.
It wouldn't be until a few issues / chapters into the overall story that Mr. Mind would actually be seen.
And from Who's Who: The Definitive Directory of the DC Universe Vol. XV (May 1986):