The list of existentialists is extremely diverse, ranging from devout Catholics, Protestants, and Jews to agnostics and staunch atheists, and includes many nationalities, temperaments and personal beliefs.
Existentialists tended to be mavericks, outsiders of the philosophical academy who wrote in untraditional ways: fiction, plays or essays, as well as traditional philosophical treatises. In fact, most of the individuals whom we classify as "existentialists" created their works before the term was even coined.
As diverse as existentialists are, there are certain affinities among them that justify grouping them together as purveyors of an existentialist view. Their greatest similarity may be their own strong devotion to individualism, and their emphasis of the individual in discussing philosophical subjects.
Most parents recognize that they are raising a young existentialist by the time their child reaches adolescence. Questions of why, how come, are you sure, and did you know, are common. Insistence upon doing things "their way" as opposed to the "common way" is observable, even as toddlers.
The subject of death, existential angst, and the many ways one might die are also curious topics for the young existentialist. Young existentialists are those precocious kids who walk up to the older relatives in the family and cross-examine them on their beliefs about everything: life, death, and the meaning of it all.