He was the Ukranian equivalent of the US Attorney General. He believes Biden coerced his removal because he was investigatng corruption at the outfit Hunter Biden was taking money from. It will be interesting to see if the mainstream media's reporting of this provides any evidence that it retains the tiniest shred of integrity.
https://theconservativetreehouse.com/2019/09/26/former-ukranian-prosecutor-viktor-shokin-sworn-affidavit-outlining-joe-biden-shakedown/