Gordon Allport was the youngest of four brothers. His father was a country physician, and the family moved to Ohio shortly after Gordon's birth. Allport was educated in Cleveland and described his family life as one based on trust, affection and the Protestant work ethic. His decision to study at Harvard University was partly due to the influence of his brother, Floyd Allport, who was a graduate student in psychology at that university. Allport took a number of courses in psychology but majored in economics and philosophy. After graduating he taught English and sociology at Robert College, Constantinople, Turkey, and in 1920 won a fellowship to study psychology at Harvard. Allport completed his PhD (on personality traits—the first such study conducted in the United States) under Herbert S. Langfield (1879-1958), who strongly influenced his general approach to psychology. Langfield had studied under Stumpf (1848-1936) at the University of Berlin and subscribed to a motor theory of consciousness (the idea that sensations, emotions and thoughts are all linked to motor processes). Personality, according to Allport, similarly involves complex linkages between physiological and mental processes.

Allport regarded personality as an integrated evolving system of habits, attitudes and traits. In his first book authored alone, Personality: A Psychological Interpretation, he classified fifty different definitions of personality and concluded that they had in common a concern for determining ‘what a man really is’. Allport's own definition of personality is ‘the dynamic organization within the individual of those psychological systems that determine his characteristic behavior and thought’. No two people are completely alike, and Allport explained this using the concept of trait, which he defined as a predisposition to act in the same way in a wide range of situations. He suggested that traits, like habits, generalize to individuals and situations. Thus, there are traits that are specific to individuals and ones that are shared by most individuals. In ‘Traits revisited’, he proposed that certain criteria define a personality trait: a trait has more than nominal existence; a trait is more generalized than a habit; a trait's existence can be established empirically; traits are only relatively independent of one another; a trait is not synonymous with moral or social judgements; a trait may be considered in the context of either the personality that contains it or its distribution in the general population; acts that are inconsistent with a trait are not proof of the nonexistence of the trait. In his early work Allport distinguished between common/dimensional/ nomothetic traits—characteristics shared by a number of people in a particular culture—and individual/morphological traits—characteristics peculiar to individuals that do not allow comparisons among people. Later he considered that using the term ‘trait’ in connection with both individual and common characteristics caused unnecessary confusion, and he called individual traits ‘personal dispositions’ and common traits simply ‘traits’. He distinguished between three types of personal disposition: cardinal dispositions (so pervasive that almost everything a person does can be traced to its influence), central dispositions (generalized characteristics of a person - the ‘building blocks’ of personality), and secondary dispositions (less consistent and generalized, e.g. food and fashion preferences).

For Allport the unifying core of the personality is the self (‘the proprium’), which strives to realize its potentialities and life goals. Allport regarded the person as motivated more by social than by physiological influences and as constantly striving to become something new and different. The core of his personality theory, the self, he saw as an awesome enigma, but with characteristic tenacity he set this concept within trait theory and then proceeded to define ‘the proprium’. The latter consisted of seven subjective aspects of the self: the sense of bodily self, self-identity, self-esteem, self-image, the extension of the self, the sense of striving and the self as a rational being. This, together with a theory of motivation which overcame the limitations of homeostatic explanations, enabled Allport to formulate a detailed theory of personality based on the ideas of an earlier book, Becoming: Basic Considerations for a Psychology of Personality. Allport took the view that a person's basic convictions about what is and is not of real importance in life are founded on values, and he proceeded to identify and measure basic value dimensions. This lead to the development of the widely used multidimensional personality test, the Study of Values.

Gordon Allport's collection of essays entitled The Person in Psychology provides a good indication of his wide field of interest, not only in personality, but in mental health, prejudice, religion and fundamental methodological problems of psychology. He attempted to grasp the complexity of human beings set in the context of a social environment, and in so doing he resolutely refused to settle for the fashionable dogmas of his profession. He demonstrated a firm belief in an ‘imaginative and systematic eclecticism’. His most influential work, Personality: A Psychological Interpretation, offered a survey of what he called ‘the most important fruits of psychological research’, and is distinguished by its attempt to provide a theory embracing the results of this research. It appeared later in a much revised form as Pattern and Growth in Personality, in which he once again demonstrated an undogmatic but relentless concern for precision and finesse in pursuit of the intricacies of human personality. In his own words, he refused ‘to close off or discourage any avenue of approach to the investigation of human nature’. Although he is often referred to as ‘the dean of American personality study’, his theory of personality has attracted a modest degree of research interest. There are two reasons for this: first, the theory makes extensive use of somewhat loosely defined concepts (e.g. propriate striving, personal disposition), and second, the linkages between traits and the development of the proprium are not clearly specified. Nevertheless Allport's ideas have had a profound impact in promoting idiographic methods for studying people.

The idea of ‘Becoming’ as contrasted to ‘Being’ is central to Allport's work, and this aligned him with the so-called ‘third force’ or humanistic psychologists, although his thoughtful eclecticism allowed him to accept parts of both the psychoanalytic and behaviourist viewpoints in his developing framework. This open system, as he called it, mapped out and refined in twelve books and 228 other publications, laid the basis for a psychology of the human being. Perhaps of all his publications, the most fascinating is his departure from ‘abstractions about personality-in-general’ to an attempt to explain a ‘single concrete life’. In the idiographic Letters from Jenny (1965), he provided a unique teaching instrument for subsequent generations of students.