Gumdo is the Korean version of Kendo.
Not quite right.
1st: the words 'Gumdo' and 'Kumdo' (alternate spelling) are the Korean pronunciations for the same Chinese characters that, in Japanese, spell 'kendo'. All three words translate as roughly 'the way of the sword'. In Japan, the word 'kendo' refers to the martial sport that uses a bamboo sword and cloth armor for sparring. In Korea, the word 'kumdo' still retains its much more generic meaning, and so it refers to ANY sword martial art. Thus, 'Gumdo' or 'Kumdo' CAN refer to the martial sport that uses a bamboo sword for sparring (identical to kendo), but it can also refer to iaido, kenjutsu, haidong gumdo, shimgumdo, muye eship saban, sip pal gi, and dozens of other sword arts. To differentiate between this among English-speakers, those who practice Korean kendo usually use the spelling 'Kumdo', and those who practice other sword arts usually use the spelling 'Gumdo' (with a few exceptions), even though they are still the same words in Korean. Not lost yet? Good, there's more!
2nd: I assume the OP referred to the martial art of Haidong Gumdo (Also spelled 'Haedong Gumdo' or Haedong Kumdo' - one of those exceptions mentioned above). The term 'Haidong Gumdo' means 'the way of the sword from east of the sea', and refers to an ancient Chinese name for the Korean kingdom of Palhae. So, basically, the name means Korean swordsmanship. This name was first used around 1982 by the co-founders of the art, Kim, Jong Ho and Na, Han Il. Up until this time, they taught the same art under the name 'shim gumdo', although there is an art called by that name that is quite different (hence the name change). The sword methods themselves, as well as certain formalities and elements of etiquette/style, reflect an older root, but the formalized curriculum was established by GM/President Kim around this time.
GMs Kim and Na studied Korean swordsmanship from the early 1970's, and were both licensed to teach the Korean sword arts of Gicheon Mun ('Gateway to Heavenly Energy', a secretive, almost cult-like soft-style, internal MA based on Northern Chinese mantis KF forms) and shimgumdo. The Grandmaster of Gicheon at that time (who has some title like, 'Exalted Supreme Human being') was teaching as early as the 1950's. This is as far back as I have been able to trace the history and lineage of the art.
There were two large waves of Northern Chinese KF schools that came into Korea, one in 1949, and the other in the late 18th century. It is possible that either (or some combination of both) contributed to the formation of Gicheon as a martial art, providing the root for modern haidong gumdo.
Some websites provide a fanciful 'secret school in the mountains 2000 years ago in ancient Koguryeo' history. This is fictitious. As far as I can tell, there were no 'Samurang' warriors, although the Koguryeo Kingdom did defeat a million-man Sui Chinese army, but by damming a river until their adversaries were mid-stream in crossing, NOT by their superior sword skill.
References and more info available on request.