Inflaton is a hypothetical particle proposed in cosmology to explain the rapid expansion of the universe during the inflationary epoch, a brief period just after the Big Bang. This expansion is thought to have smoothed out the universe, making it more uniform and leading to the large-scale structure we observe today. The concept of inflaton is tied to quantum field theory, where it is considered a field that permeates space. As this field fluctuates, it can create energy that drives the exponential growth of the universe, helping to resolve several puzzles in cosmology, such as the uniformity of the cosmic microwave background radiation.