Across the course of the game's development, the races and graphics of StarCraft have changed drastically from Chris Metzen's original concept art. In particular, since their initial public debut at E3 1996, the Zerg have seen extensive changes to their visual design. This was primarily due to Blizzard's attempt to steer the game away from the visual appearance, unveiled at the 1996 E3, that had earned the game a derisive label of "Warcraft in space". The Zerg were originally known as the "nightmarish invaders", later becoming the "Zurg", and then renamed again to its current spelling to avoid any potential trademark conflicts with Pixar's Toy Story character of Emperor Zurg. In the early alpha versions built by Bob Fitch, the Zerg still showed their insect-inspired base, but their appearance was heavily dominated by spikes and bright shades of blue and purple. Early Protoss concept art showed a green and blue color scheme in their mechanical armor. Closely hewing to the familiar visual style of Warcraft II: Tides of Darkness, the build received much criticism from industry press, prompting a redesign of the game engine and an overhaul of the races' respective visual designs.