Kim Jong Il was the second Leader of North Korea [the DPRK], and was commonly referred to as The Dear Leader. He held this position from 1994 to 2011, when he died. He was the son of Kim Il Sung, the first Leader of the DPRK. Kim Il Sung has died, but he is still the official Head of State, known as The Eternal Leader.
The DPRK has a Communist ideology and close ties to the People's Republic of China. The entire economy is controlled by the government. Starting with Kim Il Sung, the Leader has operated in a Cult of Personality, in which he is virtually worshiped by the people, and everything is done in his name.
Anybody who does not show enough devotion to the Leader, or whose devotion seems insincere, can be sent to a re-education camp to be brainwashed. [The term brainwashing actually comes from the Chinese Communist concept of cleansing the mind from old corrupt ideas.] Thus the Leader is identified with the nation. For instance the Mass Games [DPRK Athletic competitions on a grand scale] are done in honor of the Leader.
During the 1990s there was a terrible famine in the DPRK due to mismanagement. To recover from this, Kim allowed very limited free-market trading in the DPRK. During Kim Jong Il's administration, the DPRK was judged to have one of the worst human rights records in the world.
In spite of making an agreement with the US to cut back on nuclear weapons in exchange for aid, Kim later tested a nuclear weapon.
When he died in 2011, his son Kim Jong Un became the leader.