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.
KLOE (experiment)
Data from the original experiment allowed Makoto Kobayashi and Toshihide Maskawa to give the most precise measurement of one of the elements of the quark mixing matrix currently available. They then used this value to discover "the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature", which won them the Nobel Prize in Physics in 2008.