Erik Erikson (1902-1994) became one of the earliest psychologists to take an explicit interest in identity. The Eriksonian framework rests upon a distinction among the psychological sense of continuity, known as the ego identity (sometimes identified simply as "the self"); the personal idiosyncrasies that separate one person from the next, known as the personal identity; and the collection of social roles that a person might play, known as either the social identity or the cultural identity. Erikson's work, in the psychodynamic tradition, aimed to investigate the process of identity formation across a lifespan. Progressive strength in the ego identity, for example, can be charted in terms of a series of stages in which identity is formed in response to increasingly sophisticated challenges. The process of forming a viable sense of identity for the culture is conceptualized as an adolescent task, and those who do not manage a resynthesis of childhood identifications are seen as being in a state of 'identity diffusion' whereas those who retain their initially given identities unquestioned have 'foreclosed' identities (Weinreich & Saunderson 2003 p7-8). On some readings of Erikson, the development of a strong ego identity, along with the proper integration into a stable society and culture, lead to a stronger sense of identity in general. Accordingly, a deficiency in either of these factors may increase the chance of an identity crisis or confusion (Cote & Levine 2002, p. 22).

Who was one of the earliest psychologists to take an explicit interest in identity?