Correction: Павел Андреевич Чеков Pavel Andreevič Čekov was not part of the original crew of the NCC-1701. He was added during season 2 when when sulu was busy making a movie.

It has also been said:

Star Trek creator Gene Roddenberry stated for the series’ 25th anniversary special that he created Chekov’s character in response to a Pravda article that noted that although the Soviet Union was a leader in space exploration, the international crew of the Enterprise lacked a Russian character. Including someone from Russia, the United States’ long-time Cold War adversary, matched well with Roddenberry’s vision of an ideal future in which the people of the Earth were united. (This story had actually been published in TV Guide after the character was introduced.)

but who knows if it is true