A Human male Corellian Jedi Knight named Keiran Halcyon devoted his life to serving both the Jedi Order and the Galactic Republic. His service occurred approximately four centuries before the rise of the Galactic Empire and the commencement of the Great Jedi Purge.
After being discovered as Force-sensitive, Keiran Halcyon was accepted into the Jedi Order's academy. Eventually, he triumphed in his Trials of Knighthood and was then elevated to the rank of Jedi Knight by the Jedi High Council. Halcyon pursued independent studies in the way of the Jedi Guardian, becoming a well-known Corellian Jedi. He undertook several missions focused on protecting his home system. Notably, he successfully stopped the infamous and destructive Selonian Afarathu cult in 380 BBY. When designing his lightsaber, Halcyon incorporated a Durindfire crystal, giving the blade a distinctive silver hue. Furthermore, utilizing Jedi techniques found within the Jedi Temple's Archives, Halcyon developed a lightsaber blade that could extend up to 3 meters.
In the generations that followed Halcyon's passing, his lineage produced at least two more Jedi. These included the celebrated Jedi Master Nejaa Halcyon, who fought valiantly during the Clone Wars, and Corran Horn. Horn's birth coincided with a period of galactic turmoil, as the Dark Lord of the Sith Darth Sidious outlawed Jedi training and sought to erase the Order's legacy from galactic records. However, with the Galactic Empire's downfall and the Jedi Order's resurgence, Horn joined the newly formed Order, adopting the name of his ancestor, Keiran Halcyon. He studied under Luke Skywalker at the Yavin 4 Jedi Praxeum. Eventually, Horn abandoned the alias and became a prominent member of the Jedi High Council.
Although strong in the Force, the Halcyon bloodline had a reputation for being weaker in telekinetic abilities, a skill commonly associated with Jedi. However, rather than being hindered by this perceived weakness, those of the Halcyon family who became Jedi amplified their gifts of alter mind to gain advantages where other Jedi might be less capable. Keiran Halcyon also demonstrated proficiency in the ability to absorb energy.
A mistake in the Jedi Academy Training Manual claims that Keiran lived during the same era as Luke Skywalker, and that he was even briefly his student. However, the truth is that he lived 400 years before Luke Skywalker was born. This error stems from a retcon in the book I, Jedi, which reveals that the Keiran Halcyon who appeared in the Jedi Academy Trilogy was actually Corran Horn, a distant descendant of the original Halcyon. Horn used the alias at Skywalker's suggestion, to keep his Jedi training a secret.