Looking back on the development of the universe in the context of our present scientific understanding, we believe that the universe began with the big bang and subsequently expanded and cooled. Increasingly more complex forms of matter began to emerge as temperatures dropped sufficiently to allow matter to bind. Early on, the universe consisted of a plasma that included deconfined quarks and gluons. Within microseconds after the big bang, the temperature had decreased sufficiently for the strong force to bind the quarks and gluons into hadrons. With further cooling, nucleosynthesis followed and eventually electrons joined nuclei electromagnetically to form neutral atoms. After this stage, the gravitational force began to dominate the universe. A primary goal of relativistic heavy ion physics is to produce, detect, and describe the quark-gluon plasma (QGP) phase. Towards this end, four experiments have been built at RHIC: BRAHMS [1], PHENIX [2], PHOBOS [3], and STAR [4]. This paper describes experimental results from the first three years of experiments at the Relativistic Heavy Ion Collider with a strong focus on data taken with the PHENIX detector.