Lee Myung-bak is the fifth former South Korean president to be investigated by the prosecution.
Park Ji-won has more on the former presidents who have been summoned in the past.

Former President Lee Myung-bak is the nation's fifth former president to have been summoned by prosecutors.
Prior to Lee,... the most recent former president investigated was former President Park Geun-hye.
About a year ago,... Park,... 11 days after being impeached for abuse of power by the Constitutional Court,... appeared for questioning by the prosecution on allegations of corruption and bribery.
She was questioned for more than 21 hours on the day,... longer than any other first-day questioning of a former president by prosecutors.
She is now awaiting next month's verdict on her criminal charges.
Back in 2009,... former President Roh Moo-hyun,... months after his presidential term ended,... was summoned by prosecutors for alleged bribery during his time in office and underwent 13 hours of questioning.
Before the second round of questioning, Roh committed suicide,... and the case on him was suspended.
In 1995,... former President Roh Tae-woo,... a couple of years after his term ended,... was summoned on charges of receiving hundreds of millions of dollars in bribes from business tycoons.
After one more round of investigations, he was arrested.
Later he was sentenced to 12 years in prison following additional charges of mutiny,... but was given a presidential pardon two years later.
In late 1995,... ex-President Chun Doo-hwan,... who didn't comply with the prosecution's summons,... was arrested on charges of mutiny, treason and corruption,... and was sentenced to life in prison.
Chun was also given a presidential pardon by the Kim Young-sam administration in 1997.
Park Ji-won, Arirang News.