Star Trek Canon Special Note
Not everything listed in the origin is Canon. That is because only television shows and movies are considered canon. This being a comic website there are many things here that are not canon. So unless it is contradicted in film it should be listed as part of the character biography.
Pavel Chekov first started his service on board the Enterprise as the ship's navigator. Chekov served for decades on the Enterprise's voyage, even filling in for Spock at the science station when he was gone or busy. Later Chekov was transferred over to the USS Reliant and was promoted to lieutenant.
Chekov and the Reliant's Captain Clark Terrell went to the planet Ceti Alpha VI to look for a suitable testing zone for Project Genesis. Project Genesis was designed to rearrange matter on a world to make it suitable for living and habitats. While there they were captured by Khan Noonien Singh and his followers.
Khan revealed to them that they were not on Ceti Alpha VI but on Ceti Alpha V. Khan was a genetically engineered man who ruled the 20th century Earth. When Kahn was defeated and overran he escaped onto a sleeper ship, where they were later discovered by Captain James Kirk. Khan tried to take over the Enterprise so Kirk had Khan and his followers marooned onto Ceti Alpha V. Kirk thought it would be a good planet for Khan and his men to live on but shortly after they were left there Ceti Alpha VI exploded and caused the destruction of Ceti Alpha V's ecosystem.
Ceti Alpha V was left a stormy desert planet. Most of the survivors were killed by a creature called the Ceti eel, including Khan's wife. Ceti Alpha V's orbit had shifted and caused the Reliant to believe it was Ceti Alpha VI. Ever since Khan has been dwelling for revenge against Kirk for the death of his wife. Khan than implanted the mind controlling Ceti eel's through Chekov and Clark's ears to their cerebral cortex. Khan uses them to steal the Reliant, where he discovers information about Project Genesis. Khan believes he could use Genesis as a weapon to get revenge, so he sets out to steal it. When Chekov is ordered to kill Kirk he overcomes it's control and faints, causing the eel to leave its brain.
Chekov later joins the crew of Enterprise-A as Second Officer and Navigator, eventually reaching the rank of Commander. After retiring from Starfleet, he attended the U.S.S. Enterprise-B's maiden voyage, the mission where Kirk was presumed dead.
Chekov was created for the television show Star Trek. Being a product of the 1960's, the character was added for sex appeal based on the looks of rock stars like the Monkeys. Checkov was only in two of the three seasons of the original series and did not appear in any of the cartoon series.
Major Story Arcs
The Mirror Universe.
In the Mirror Universe Chekov tries to kill Captain Kirk to move up in rank. He is tortured and then later pardoned by Kirk who had been disguised as the mirror Kirk.