Development of the series began in early 2010 with the announcement that Alex Kurtzman and Roberto Orci, screenwriters of the first two live-action films, would be creating the series. Casting began soon after with the announcement that Peter Cullen and Frank Welker would reprise their roles as Optimus Prime and Megatron. According to executive producer Jeff Kline the two characters, along with Bumblebee, were considered “must-haves” for the series. From that point on, they tried to include characters that would complement their personalities “rather than emulate them”. From the early stages of development, a story bible had been created so that writers had a basic idea of where the plot was heading. Early in development, it was announced that the first season would consist of 26 episodes—the first five airing as a miniseries from November 29, 2010 to December 3, 2010. The remaining episodes aired from February 11, 2011 to October 11, 2011. While the first season was still running, it was announced the show had been renewed for a second season, also consisting of 26 episodes.