The notion of a "set that contains all sets which do not contain themselves" is a paradoxical idea attributed to which English philosopher?

The story behind the answer

Bertrand Russell identified the paradox of the “set of all sets that do not contain themselves” (1901). If such a set R exists, asking “Does R contain itself?” yields a contradiction: if it does, it must not; if it doesn’t, it must. This showed that “naive” set theory—where any definable collection is a set—leads to inconsistency.

Russell’s discovery shook the foundations of mathematics, prompting Frege to revise his system and inspiring new foundations like Zermelo–Fraenkel set theory and Russell’s own type theory. A handy memory hook is the “barber paradox”: the barber shaves all and only those who do not shave themselves—so who shaves the barber? Both puzzles illustrate self-reference leading to contradiction, a core idea in logic.