Greatness is a concept of a state of exceptional superiority affecting a person or object in a particular place or area. Greatness can also be attributed to individuals who possess a natural ability to be better than all others. An example of an expression of the concept in a qualified sense would be "Hector is the definition of greatness" or "Napoleon was one of the greatest wartime leaders". In the unqualified sense it might be stated "George Washington achieved greatness within his own lifetime", thus implying that "greatness" is a definite and identifiable quality. Application of the terms "great" and "greatness" is dependent on the perspective and subjective judgements of those who apply them. Whereas in some cases the perceived greatness of a person, place or object might be agreed upon by many, this is not necessarily the case, and the perception of greatness may be both fiercely contested and highly idiosyncratic.

Historically, in Europe, rulers were sometimes given the attribute "the Great", as in Alexander the Great, Frederick the Great, Alfred the Great and Catherine the Great. Starting with the Roman consul and general Pompey, the Latin equivalent Magnus was also used, as in Pompeius Magnus, Albertus Magnus, and Carolus Magnus. The English language uses the Latin term magnum opus, (literally "great work") to describe certain works of art and literature.

Since the publication of Francis Galton's Hereditary Genius in 1869, and especially with the accelerated development of intelligence tests in the early 1900s, there has been a vast amount of social scientific research published relative to the question of greatness. Much of this research does not actually use the term great in describing itself, preferring terms such as eminence, genius, exceptional achievement, etc. Historically the major intellectual battles over this topic have focused around the questions of nature versus nurture or person versus context. Today the importance of both dimensions is accepted by all, but disagreements over the relative importance of each are still reflected in variations in research emphases.

Early scientific research on greatness had a strong genetic emphasis and focused on intelligence as the driving force behind the concept.

The earliest such research, Hereditary Genius, by Francis Galton (1869), argued that people vary hugely in "natural ability" which is allegedly inherited biologically. Those at the very top end of the range, i.e., geniuses, become according to Galton the "eminent" achievers of their generation. To prove this thesis Galton collected data showing that genius clusters in what he termed "Notable Family Lines", such as those of Bernoulli, Cassini, Darwin, Herschel, and Jussieu in science, or Bach in music.

Galton then calculated the odds of eminent people having eminent relations, taking into account the closeness of the biological connection (e.g., son vs grandson), and the magnitude of achievement of the eminent parent. His findings were as anticipated: the more famous the parent (i.e., the greater level of presumed "natural ability"), the greater likelihood there would be illustrious relatives; and the closer the blood tie, the greater those odds.

Catharine Cox's book on The Early Mental Traits of Three Hundred Geniuses (1926), was similar to Galton's in its orientation. Using the method that her mentor, Stanford Psychology Professor Lewis Terman, had developed for differentiating children in terms of intelligence, Cox coded records of childhood and adolescent achievements of 301 historic eminent leaders and creators to estimate what their IQs would have been on the basis of intellectual level of such achievements relative to the age at which they were accomplished. For example, John Stuart Mill reportedly studied Greek at 3, read Plato at 7, and learned calculus at 11. As such, what he was doing at 5, the average person couldn't do until 9 years, 6 months of age, giving Mill an estimated IQ of 190.

Cox found that the perceived eminence of those with the highest IQs was higher than that of those attaining lower IQ estimates, and that those with higher IQs also exhibited more versatility in their achievements. For example, da Vinci, Michelangelo, Descartes, Benjamin Franklin, Goethe, and others with IQs in the mid 160s or above were superior in their versatility to those attaining lower scores, such as George Washington, Palestrina, or Philip Sheridan.