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Galen Erso was one of the secondary tritagonists of the movie Rogue One: A Star Wars Story. A human male, he was a scientist who had been forced into working for the Galactic Empire.
Galen was the husband of Lyra and the father of Jyn Erso.
Due to his expert knowledge of Kyber Crystals, Galen was kidnapped by Director Orson Kemmic after Kemmic killed his wife. Jyn hid in a nearby cave until family friend Saw Gerrera arrived. With Galen and Lyra gone Saw took responsibility for Jyn.
Knowing that the Empire could complete the Death Star without his help, Galen decided to proceed with helping them, but built a critical design flaw into the station. After the station was completed he passed the information on to a defecting pilot. The defecting pilot went to Saw Gerrera, who in turn provided the message from Galen to his daughter. The details of his sabotage was buried in the technical readout, which Jyn was able to steal and transmit to the Alliance.
Galen died during a Rebel attack on the installation where he was being held. He managed to live long enough to see his daughter one last time.
Galen was successul in his plans to have the Death Star destroyed. Working off the information in the plans the Alliance found the exhaust port he had built in to the Death Star. Luke Skywalker was able to fire torpedoes down the port, destroying the superweapon before it could cause the deaths of any more innocents.