The Pokémon World Championships began in 2004 with the Pokémon Trading Card Game. The inaugural championship was held in Orlando, Florida, at the Wyndham Palace Resort and Spa.
The event created a global competition for top Pokémon TCG players, who qualified through organized tournaments and competed in age divisions. The original divisions were Juniors, Seniors, and Masters, allowing younger players and adults to compete within appropriate categories.
Video game competitions were added later. Play! Pokémon began organizing tournaments for the Pokémon video game series in 2008, and these became known as the Video Game Championships, or VGC. The TCG and VGC competitions now culminate at the broader Pokémon World Championships.
The first championship is sometimes dated to 2008 because that was when video game competition joined the official world-championship structure. However, the Pokémon World Championships themselves began in 2004 through the TCG. That distinction makes 2004 the precise answer to the question.