Strange quark
The first strange particle (a particle containing a strange quark) was discovered in 1947 (kaons), but the existence of the strange quark itself (and that of the up and down quarks) was only postulated in 1964 by Murray Gell-Mann and George Zweig to explain the Eightfold Way classification scheme of hadrons. The first evidence for the existence of quarks came in 1968, in deep inelastic scattering experiments at the Stanford Linear Accelerator Center. These experiments confirmed the existence of up and down quarks, and by extension, strange quarks, as they were required to explain the Eightfold Way.
George Zweig
As pointed out by astrophysicist John Gribbin, Gell-Mann deservedly received the Nobel Prize for physics in 1969, for his overall contributions and discoveries concerning the classification of elementary particles and their interactions; at that time, quark theory had not become fully accepted, and was not specifically mentioned in the official citation of the prize. In later years, when quark theory became established as the standard model of particle physics, the Nobel committee presumably felt they couldn't recognize Zweig as the scientist who first spelled out the theory's implications in detail and suggested that they might be real, without including Gell-Mann again.
Nevertheless, in 1977 Richard Feynman nominated both Gell-Mann and Zweig for the Nobel prize, presumed to be his only
nomination for such.
Whatever the reason, despite Zweig's contributions to a theory central to modern physics, he has not yet been awarded a Nobel prize.