His maternal grandfather, Lee Won-jun, was a bureaucrat who served as the governor of South Hamgyeong Province during the Japanese colonial period. In 2014, controversy arose when Yoo's family members visited the Japanese Embassy in Seoul to protest the screening of the film "The Merciless" in which Yoo starred, citing his maternal grandfather's past actions.
We haven't written up this one. Hankyoreh has the full story — the link below goes straight to it.