Juche was introduced in 1983, as a replacement for Ko-Dang. General Choi developed the pattern to reflect some of the new techniques that had been perfected in more recent years; while it contains many of the same movements as Ko-Dang it also includes the slow motion kicks, two direction kick, dodging kicks and flying hand attacks. It is also said to challenge the 2nd degree more, as Kodang was considered to be comparatively easy.

In an interview conducted during a visit to Britain in November 1999, General Choi stated: "As new techniques were developed they needed to be represented in the patterns. The pattern Kodang was replaced simply because it represented the latest Korean history, basically last in first out."[1]

General Choi's final years were marked by his efforts to end the seperation between North and South Korea. He introduced Taekwon-Do to North Korea in 1980, and in 1983 he won further favour with the North Korean leader, Kim Il-sung, by changing one pattern from Ko-Dang (named after Cho Man-sik, a North Korean democratic Christian moderate) to Juche (after the isolationist policy of "self-reliance" invented and advocated by Kim Il-sung [2]). Though Choi's intention had presumably been reconciliatory, due to the political climate it went down rather badly in South Korea (which, incidentally, was a repressive military dictatorship at the time under General Chun Doo-hwan, who had seized power in a coup d'état in 1980).

Other commentators, however, point to a more practical motive, claiming the change was made to seek favour with Kim Il-sung in return for financial backing

There is still considerable discussion revolving around the use of these two patterns. While Juche is the official pattern given in the ITF syllabus, some clubs (generally the more traditional ones) teach Ko-Dang instead, while some others teach both. The situation is further complicated when organisations require Juche, but allow students to perform Ko-Dang under certain conditions related to age or physical disability; and became downright farcical at the 2004 World Championships in South Korea when competitors performed Juche but called it Ko-Dang so as not to offend the hosts. On the 22 July, 2005, The ICTF executive decided to consider officially changing the name of Juche to Chang-Hon, and later announced that this had been agreed; but in 2010 Master Stanley of the ICTF revealed that, after careful consideration, this decision had been reconsidered [3]. Following on from this, on 24th June 2008 [4] GM Choi's ITF-C branch announced that they were officially renaming pattern Juche to Ko-Dang, while still keeping the moves as in Juche (with the exception of the dodging reverse turning kicks, which have been changed to jumping reverse hook kicks), thus causing yet more confusion. It is not known at this time whether the other two branches will follow, but it seems unlikely.

References:

[1] - Interview with General Choi
[2] - Juche on Wikipedia
[3] - Ask Master Stanley
[4] - Tul Update

Recommended Reading:

Biography of Cho Man-sik
USTF Newsletter, 17/09/2005 (pdf)
Juche Versus Ko-Dang: Black Belt Thesis by Mr. Dalton VI, IUTF
ITF: Evolution or Separation? Part 2: The changing of Ju che by Master Anslow