Park Chung-hee
The election is being closely watched at a time of high tensions with North Korea.
“The case is very grave as the suspect has demonstrated acts of abuse of power," the prosecutors' office says.
Paul Ryan said he hopes to be finished by the April recess.
Park Geun-hye is the country's first democratically elected leader to be forced from office.
WHAT'S HAPPENING
The indictments are the latest twist in a corruption scandal that has gripped the country for months.
And he called NATO "obsolete."