Clayton Paul Alderfer (born September 1, 1940 in Sellersville, Pennsylvania) is an American psychologist who further developed Maslow's hierarchy of needs by categorizing the hierarchy into his ERG theory (Existence, Relatedness and Growth). This theory posits that there are three groups of core needs (existence, relatedness, and growth), hence the label, ERG theory.
The existence group is concerned with providing our basic material existence requirements. They include the items that Maslow considered to be physiological and safety needs (Figure 1). The second group of needs is those of relatedness, the desire we have for maintaining important interpersonal relationships. These social and status desires require interaction with others if they are to be satisfied, and they align with Maslow's social need and the external component of Maslow's esteem classification. Finally, Alderfer isolates growth needs, an intrinsic desire for personal development. These include the intrinsic component from Maslow's esteem category and the characteristics included under self-actualization.
Alderfer categorized the lower order needs (physiological and safety) into the existence category. He fit Maslow's interpersonal love and esteem needs into the relatedness category. The growth category contains the self-actualization and self-esteem needs. Alderfer also proposed a regression theory to go along with the ERG theory. He said that when needs in a higher category are not met, then individuals redouble the efforts invested in a lower category need. For example, if self-actualization or self-esteem is not met then individuals, will invest more effort in the relatedness category in the hopes of achieving the higher need they lack.