K-2SO is a fictional male in the Star Wars series. The character was portrayed on screen by Alan Tudyk. His allegiance / loyalty is to The Rebel Alliance. K-2SO (Kaytoo Esso) was once a Galactic Empire droid that's been converted to work for Rebel Alliance. K-2SO is used by the Rebel Alliance to steal the Death Star plans. K-2SO first appears congratulating Jyn Erso on being rescued, one of many comical lines from the robot. The robot is reminiscent of the droid in Jabba, the Hutt's palace that wanted to put a restrainer belt on R2-D2 at the time he was torturing another droid. The droid is extremely funny compared to every other comical character that has gone before.
K-2SO is not the only robot of his model, there are others including one that the Rebels destroy. K-2SO remarks that after the rebels destroy the other robot that they did know it wasn't him and they reply they did.
K-2SO does share some traits that C-3PO has such as having the knack of giving chance of success percentages. He acts as though he's human. Cassian Andor gave the K-2S0 an instruction to stay on the ship but he betrayed his captain which was just as well because K2-SO saved the lives of Cassian and Jyn Erso in doing so.
Kaytoo is played in stop motion by actor Alan Tudyk who has been on screen as Wash Warren in the Firefly series as the ships pilot. Again Alan does play a pilot in this film.
Where they tried to make Jar Jar Binks the comedic character in the prequels and failed dismally. They have learnt their lesson and made K-2SO into a very funny character without the stupid acting, they just relied on his wit and one liners.
Sadly, K-2SO will not be returning for any future film as he was killed off when Stormtroopers stormed the computer control room that he was in. K-2SO was able to fight off and give Cassian and Jym Erso the time that they needed to get the item and broadcast the plans to the Rebel Alliance in orbit round Scarif.