ATLAS is one out of four large experiments at the Large-Hadron-Collider (LHC) at CERN in Geneva. It is dedicated to a comprehensive study of very high-energy proton-proton collisions at the terascale. A primary goal is the search for new phenomena beyond the horizons of the known Standard Model of particle physics. Such phenomena will crucial for the understanding of the development of the early universe at times as small as 10-12 seconds after the Big Bang.