The man who staged a shock attack on the US ambassador to South Korea is a convicted, maverick political activist whose blog writings display a profound anger towards "foreign powers" like the US and Japan.
Kim Ki-Jong, 55, was known to police after having been handed a two-year suspended sentence in 2010 for hurling a rock at the then Japanese ambassador to South Korea.
He runs a small activist group known as "Our Backyard" which has a strong nationalist agenda, and pushes for close engagement with North Korea in order to reunify the divided Korean peninsula.
South Korea has a number of militant activist groups -- of differing sizes -- that inhabit the left- and right-wing margins of the political spectrum and regularly engage in vocal and sometimes violent public protests.
As he was wrestled to the ground after his knife attack on Ambassador Mark Lippert, Kim shouted slogans against the annual US-South Korea joint military exercises which kicked off on Monday.
The drills, known as Foal Eagle and Key resolve, always trigger a surge in tensions with North Korea which condemns them as rehearsals for invasion.
"I plotted the whole thing alone for 10 days... I made the sacrifice to stop Key Resolve," Kim told police according to the Yonhap news agency.
In his postings on his group's blog, Kim complained that the military exercises were blocking all efforts to resume a North-South Korea dialogue.
'Plots by foreign powers'
"I'm so saddened by this reality in which... we keep fighting against each other while being swayed by plots by foreign powers," he wrote.
A Unification Ministry official told AFP that Kim had visited North Korea at least half a dozen times between 2006 and 2007.
He also tried to erect a memorial in Seoul to the late North Korean leader Kim Jong-Il after his death in late 2011, but was blocked by police and conservative activists.
Pictures on the blog showed images of Kim protesting in front of the US and Japanese embassies in Seoul over a number of issues.
He also ran campaigns to denounce Japan in its territorial dispute with South Korea over small Seoul-controlled islets in the Sea of Japan (East Sea).
It was during one such protest in 2010 that he hurled a rock at the Japanese ambassador and was arrested.
He later self-published a small book about the incident that laid out his motives and views on what he perceived to be Japanese aggression.
He reportedly had a number of other brushes with the law, mainly involving violent behaviour during public protests.
There are nearly 30,000 US troops permanently stationed in South Korea and anti-US sentiment -- often fuelled by left-leaning groups -- has waxed and waned over the decades since the 1950-53 Korean War.
But surveys show overwhelming public support for the South Korea-US military alliance.
The attack on Lippert carried echoes of a 2006 assault on President Park Geun-Hye when she was a legislator.
A 50-year-old man slashed Park across the face with a blade while she was out campaigning for a local election.
He was convicted of attempted murder and jailed for 10 years.