The positron is the antimatter analog of the electron. The antiproton is the antimatter analog of the proton.
Antimatter is observed in cosmic rays and can be created from energy in the laboratory.
It occurred about 15 billion years ago and generated the expanding motion that we observe today. See also critical density. The horizon lies at a distance in light years equal to the age of the Universe in years. If the density of the Universe exceeds the critical density, the Universe will stop expanding and collapse. If the density is less than the critical density, the Universe will expand forever.