(CNN)The suspect behind the knife attack on the American ambassador to South Korea had a long, troubled history and often blamed the U.S. for tensions in the Korean Peninsula. 

Kim Ki-Jong, 55, was quickly overpowered and taken into custody after he attacked U.S. Ambassador Mark Lippert with a fruit knife Thursday morning. 

Police say Kim's motive for the attack was to improve North-South Korean relations and to stop the annual military exercises held jointly by the U.S. and South Korea. 

It wasn't the first time Kim has taken drastic steps to make his point. 

-- In 2010, Kim was given a suspended jail sentence for hurling a concrete block at a Japanese envoy to South Korea, according to the Yonhap news agency. That incident is believed to be the first attack on a foreign ambassador in South Korea. 

-- Kim allegedly harbored sympathies for North Korea, according to Korean media reports. Yonhap reported that Kim had visited North Korea six times between 2006 and 2007, had attempted to erect a memorial for former North Korean leader, Kim Jong-il in Seoul, and once set himself on fire in front of the presidential office. 

-- He was frequently seen at protests, wearing a beret and blaming U.S. policies for straining relations between North and South Korea. 

Kim was a member of the Korea Council For Reconciliation and Cooperation, which hosted Lippert at the Thursday event where the attack occurred. The group advocates reunification of the Koreas as well as humanitarian aid to North Korea. Kim was one of its 181 members, but wasn't on the list of those invited for the event, according to police. But he was allowed in because an event staff recognized him from the organization. 
was he invited to the event?
wasn't on the list of those invited