The PhET Interactive Simulations are well-known resources that originated in physics and are now used in multiple science disciplines. Many new educational innovations are developed but do not find a large audience--PhET, however, has been successful in becoming widely-used. This is the first of several planned case studies of widely-used educational innovations to characterize the strategies used by principle investigators (PIs) to promote widespread use of their innovation. We collected multiple sources of data, including interviews with the original developers, relevant publications, and documents released by the PhET team over the years. We analyzed the interview data and documents using a predetermined lens and constructed a narrative of key events and strategies. We found the PhET team refined and solidified the simulations after a period of pilot testing, and additional funding prompted new phases of propagation. With these results we refined our framework of successful propagation. The results of this work may help future PIs design a propagation plan for their innovation.