"Pokémon"s history has been marked at times by rivalry with the "Digimon" media franchise that debuted at a similar time. Described as "the other 'mon'" by IGN's Juan Castro, "Digimon" has not enjoyed "Pokémon"s level of international popularity or success, but has maintained a dedicated fanbase. IGN's Lucas M. Thomas stated that "Pokémon" is "Digimon"s "constant competition and comparison", attributing the former's relative success to the simplicity of its evolution mechanic as opposed to Digivolution. The two have been noted for conceptual and stylistic similarities by sources such as GameZone. A debate among fans exists over which of the two franchises came first. In actuality, the first "Pokémon" media, "Pokémon Red" and "Green", were released initially on February 27, 1996; whereas the "Digimon" virtual pet was released on June 26, 1997.