Theory of 'Phychosexual Development' was formulated by:

According to Sigmund Freud, personality is mostly established by the age of five. Freud's theory of psychosexual development is one of the best known, but also one of the most controversial. In Freaudian psychology, phycholosexual developement is a central element of the psychoanalytical. Sexual drive theory, that human beings, from bih, possess an instinctual libido (sexual appetite) that develop in 5 stages - the oral, the anal, the phallic, the latent, and the genital - is characterised by the erogenous zone that is the source of the libidinal drive. Sigmund freud proposed that if the child experienced anxiety, thwaing his or her sexual appetite during any libidinal (phychosexula) deveolpement stage, said anxiety would persist into adulthood as a neurosis, a functional mental disorder. Ref: Kaplan & Sadock's Synopsis of Psychiatry, 10/e, Page 195