The term "borderline" was first used by Adolph Stern in 1938 to describe a group of patients who had characteristics of both psychotic and neurotic disorders.

In 1975, Otto Kernberg described "borderline personality organization" and its main features: a consist pattern of behavior and functioning characterized by instability that reflected a poorly integrated personality.

The present day characteristics that define borderline personality disorder were first described by J. Gunderson and J. Kolb in 1978.

Source: Borderline Personality Disorder: The NICE Guideline on Treatment and Management