Milankovitch cycles is the name given to the collective effect of changes in the eccentricity, axial tilt, and precession of the earth's orbit on the climate, resulting in 100,000 year ice age cycles of the Quaternary glaciation over the last few million years.
The Milankovitch theory is not perfectly worked out: in particular the largest response is at the 100,000 year timescale but the forcing is apparently small at this scale. Various feedbacks (from CO2, or from ice sheet dynamics) are invoked to explain this discrepancy.
Milankovitch-like theories were advanced by Joseph Adhemar, James Croll, Milutin Milankovic and others, but verification was difficult due to the absence of reliably dated evidence and doubts as to exactly which periods were important. Not till the advent of deep-ocean cores, and the seminal paper by Hayes, Imbrie and Shackleton "Variations in the earths orbit: pacemaker of the ice ages" in Science, 1976, did the theory attain its present state.