A high-flying prosecutor, who was demoted under impeached former president Park Geun-hye, is overseeing the case against her as Park made her first appearance in court on Tuesday to face criminal charges over the corruption scandal that ousted her.

Yoon Seok-youl, 57, was demoted for defying his boss's order to back off a 2013 investigation into Seoul's spy agency over its suspected efforts to illegally support Park Geun-hye's 2012 presidential bid. At the time, leading a special investigation team, Yoon pressed on with the probe anyway, arresting spy agency officials and raiding their offices.

Yoon was subsequently suspended from the investigation and demoted to relatively trivial posts outside of Seoul.