Doctor on it’s own doesn’t require research. What needs research is Ph.D for “doctor of philosophy” more specifically “philosophiae doctor.”
M.D. is “Medical Doctor” other examples are D.M.A. “Doctor of Musical Arts” for music performers and Ed.D. “Doctor of Education” which is closest to the original meaning of Doctor. You also have https://en.wikipedia.org/wiki/Doctor_of_Arts and a few others.
PS: While the Ph.D. is the most common doctoral degree in the United States, the U.S. Department of Education and the National Science Foundation recognize numerous research-oriented doctoral degrees such as the D.A. as "equivalent",[1][2] and do not discriminate between them.