Koi mil gaya is the story about Rohit Mehra (Hrithik Roshan ) who shows the world that friendship is truly universal.
Ranjay Mehra (Rakesh Roshan) is obsessed with establishing a contact with the extraterrestrial life.He invents many innovative gadgets, instruments and finally succeeds in devising a computer that can transmit messages to space.
His foresight becomes reality when as a response to this signals, a spaceship is sighted in the sky. But before Sanjay can even enjoy his success,he and his wife sonia (rekha) meet with a horrific accidents where sonia survives but sanjay loses his life.
Sanjay's son rohit is born into this world;a mentally challenged child who faces ridicule and torment at every phase of this life.His lone companion is Nisha (Priety Zinta) whose compassion draws her towards Rohit.
One day Rohit discovers his father's old computer and calls Nisha to help him use it.Both of them are completely fascinated by the image and instructions that appear on the screen and relentlessly experiment with the device; not realizing the impact this would have.
The whole town witnesses a blackout and a bizarre phenomenon… in an incandescent glowing sky… a colossal spaceship is sighted.
However more strange findings are in store for Rohit,and the audiences alike.