1) Defense mechanisms are unconscious psychological strategies used to cope with reality and maintain self-image. They arise in response to anxiety from conflicts between the id, superego, and reality.
2) Sigmund Freud first introduced the concept of defense mechanisms in the 1890s and identified several early mechanisms like denial, displacement, and repression. Anna Freud further studied defenses and classified them.
3) Defenses allow temporary respite from changes, reduce instinctual drives, mitigate unresolved conflicts, and keep anxiety within limits. They can be adaptive or pathological depending on overuse.