Personality is the value that makes each individual differ from others and, at the same time, makes someone recognisable throughout their lives. Their pathological side, personality disorders, are currently considered as dysfunctions. Differences between personalities are ubiquitous in nature and go all the way to insects. This helps us to understand that evolution had a major role in developing personality differences, depending on the strategy that was needed, in order to keep the species alive. It also shows that maladaptive traits can be useful in improving viability by enabling better survival chances or improving chances of reproduction. These mechanisms are summarised and illustrated with the help of animal and human models. Personality disorders have been studied and classified over the years, and our understanding of them has evolved. In the early 20th century, psychoanalytic theories, notably Sigmund Freud's work, influenced the understanding of personality disorders. Freud proposed that personality disorders were rooted in unresolved conflicts and disturbances during early childhood development. The most recent major update, DSM-5, was released in 2013. It introduced significant changes to the diagnosis of personality disorders. The categorical approach was maintained, but the specific personality disorders were redefined and some criteria were modified. Additionally, DSM-5 introduced an alternative model for diagnosing personality disorders - a dimensional approach. In recent years, there has been growing recognition that personality disorders exist on a continuum, with varying degrees of severity and dimensional aspects. The dimensional approach emphasizes assessing and describing an individual's specific personality traits rather than categorizing them into discrete disorders. Research is ongoing, and future revisions of diagnostic manuals may continue to refine our understanding of personality disorders, incorporating new knowledge and perspectives.