Nejaa Halcyon, a male Human from Corellia, achieved the rank of Jedi Master within the Jedi Order. During the Clone Wars, he served the Galactic Republic as a General within the Grand Army of the Republic. The Jedi High Council was unaware that Master Halcyon was married to a Corellian woman, Scerra, and fathered Valin Halcyon. While serving the Order, he became friends with the Caamasi Jedi Ylenic It'kla, who knew him as Spicewood in his memnii. Near the war's end, he was killed by the Dark Acolyte Nikkos Tyris. His family outlived him, even after the Republic's fall and the Order's dissolution. To conceal their identities from the Galactic Empire, his widow, Scerra, wed Halcyon's friend Rostek Horn and adopted his last name.
Like many Jedi of the late Galactic Republic era, Nejaa Halcyon's Force-sensitivity was identified early, leading him to Coruscant for training as a Jedi Order Initiate. He constructed a lightsaber with a silver blade and advanced through the Order's ranks, becoming a Jedi Knight by 60 BBY. After additional training as a Jedi Guardian and involvement with the Acquisition Division's recruiters, Halcyon was promoted to Jedi Master and received a Credit chip, a custom among Corellian Jedi. He later gifted this medallion to his friend Rostek Horn, a member of the Corellian Security Force.
Around 30 BBY, Master Halcyon worked with the Acquisition Division as a recruiter in the Outer Rim Territories. During this time, he discovered the Force-sensitive Twi'lek Boc Aseca. Halcyon deemed the boy too old for training on Coruscant and denied him entry into the Order. Despite his loyalty to the Order and the Jedi High Council, Master Halcyon violated the Jedi Code by marrying Scerra, a Corellian woman. They secretly had a child named Valin. Halcyon concealed his family from the Order but suspected that Grand Master Yoda knew about his child.
When the Corellian sector closed its borders during the Separatist Crisis, Halcyon led a group of Corellian Jedi to ensure the system's security. Their involvement raised questions about their loyalties. After their investigation, the group returned to the Republic, stating, "Our commitment is to the Jedi Council and the Republic, but we are Corellians and will always have a connection to our home."
During the Separatist Crisis between the Republic and the Confederacy of Independent Systems, Master Halcyon led a team of Jedi Knights to find and recapture the Scarlet Thranta, a Judicial Department corvette whose captain and crew had defected. Halcyon intercepted the ship and hailed the rogue Captain Zozridor Slayke above Bpfassh. Slayke sent his lieutenant, a Rodian named Grudo, to provoke Halcyon and fight him. While Halcyon was distracted, Slayke boarded Halcyon's ship, the Plooriod Bodkin, unnoticed. Halcyon and his crew were stranded for months with their prisoner. Halcyon was disgraced in the media and lost the respect of his peers, though his failure wasn't discussed at the Temple. After being rescued by the High Council, Halcyon was removed from command of the mission to hunt Slayke and was left without an assignment at the Temple.
As the Clone Wars began, Halcyon received minor missions but didn't lead major battles early on. In 22 BBY, he went undercover on Corellia as the scientist Ratri Tane to gather information against the Confederacy. Later, Jedi Aayla Secura and Ylenic It'kla were dispatched to find Tane and retrieve the information. They discovered Tane was Master Halcyon, completed the mission, and kept the information from the Confederacy.
Eventually, the High Council gave Master Halcyon his first major assignment. Recommended by Supreme Chancellor Palpatine, Halcyon accepted the mission and took the news that he would serve alongside Captain Zozridor Slayke with composure. He was tasked with protecting the Intergalactic Communications Center on Praesitlyn from the Confederacy. Halcyon chose Jedi Anakin Skywalker as his second in command, having become acquainted with him at the Temple. Halcyon and Skywalker devised a plan to relieve Slayke's outnumbered organization, the Freedom's Sons, but their initial plan failed. They created a rescue mission for the people on the ground, and Halcyon led a successful assault while Skywalker captured Separatist Admiral Pors Tonith.
Having regained the High Council's confidence, Halcyon was made a General in the Grand Army of the Republic. He accepted many missions and served alongside Jan Dodonna at some point. In the war's final year, Master Halcyon, Master It'kla, and "Desertwind" went to Susevfi to neutralize the Jensaarai cult. Halcyon confronted the Dark Jedi Nikkos Tyris and died in a duel. Master It'kla recovered Halcyon's lightsaber, reported his death to the High Council, and gave the lightsaber to the Galactic Museum's Jedi exhibit.
Rostek Horn told Scerra and her son about Halcyon's death. He vowed to support them, but the disbandment of the Jedi Order and the Republic's replacement by the Galactic Empire further troubled the family. Horn and Scerra married, and the family adopted the Horn surname to hide from the Empire. They adopted young Valin and called him Hal, honoring his father. They passed on Halcyon's Jedi Credit coin to his son Corran, but they didn't know much about Nejaa Halcyon's legacy until the Lusankya launched from Coruscant. Corran Horn located the lost Jedi museum and found Halcyon's lightsaber in the exhibit.
Grand Master Yoda considered Nejaa Halcyon to possess the composure of a true Jedi Master, maintaining calm even when facing skepticism from his peers. Halcyon befriended Anakin Skywalker after a few sparring sessions at the Jedi Temple, admiring his skills learned in the war and from Obi-Wan Kenobi. Halcyon confided in Skywalker about his secret marriage, which led Skywalker to reveal his own.
Like other Jedi from the Halcyon family, Nejaa Halcyon had limited telekinetic ability under normal conditions. However, he excelled at absorbing energy, such as from blaster fire or lightsaber strikes. With this energy, Halcyon could perform telekinetic feats that most Jedi could do naturally, like when he crushed a dark Jedi with the Force. Halcyon was also skilled at mental projection through the Force.