The Higgs boson is the Goldstone mode corresponding to spontaneous electroweak symmetry breaking, so it appeared at the end of the electroweak epoch. Before the electroweak epoch, all particles were completely massless and travelled exactly at the speed of light.

The Higgs boson gains mass by "eating" the Goldstone mode corresponding to spontaneous electroweak symmetry breaking, so it appeared at the end of the electroweak epoch. Before the electroweak epoch, all particles were completely massless and travelled exactly at the speed of light.