The obvious answer is Sigmund Freud, but was there a theorist before him who created a list of specific defense mechanisms? A defense mechanism can be defined as a method by which the mind protects itself from thoughts, feelings, impulses, and/or stimuli which would be damaging to its overall health.
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1$\begingroup$ I think you gave yourself the textbook answer. To assign this novelty to someone before him would take considerable [re]interpretation because Freud came up with the notion of psychological defence in the first place. $\endgroup$ – Fizz Oct 22 '17 at 21:45
