The Grysks were a sentient species of warriors originating from a planet located within the Unknown Regions of space. Largely considered mythical, the Grysks formed a nomadic society of warriors that controlled the Grysk Hegemony, an empire of their own. They communicated using a unique language and a standard script.
Chiss Grand Admiral Thrawn warned against underestimating them, stating that any retreat on their part would be a strategic decision. He considered the Grysks to be a significant danger, a threat to both the Chiss Ascendancy and the Galactic Empire.
Jixtus, a Grysk, commanded the Grysk army that tried to overthrow the Chiss Ascendancy, but Senior Captain Thrawn and Admiral Ar'alani killed him.

The Grysks were a species shrouded in myth, rarely seen by outsiders. They possessed a common script and an uncommon language. Tales depicted them as nomadic wanderers in starships so numerous they could obscure stars, and as fearsome warriors who relied on overwhelming numbers and aggression.
Thrawn, a Grand Admiral of the Galactic Empire from the Chiss Ascendancy, cautioned against accepting these stories at face value, considering the potential biases of artists. He suggested that their victories stemmed from unique tactics and weaponry, rather than sheer numbers. Thrawn also questioned the nomadic aspect of their culture, arguing that most species originating on planetary bodies are reluctant to abandon them. Furthermore, artistic depictions of their starships indicated a preference for environments with sun, sky, and soil, rather than the emptiness of space.
The Grysk Hegemony was the name of the empire they governed. The Grysks utilized "client species," individuals they had manipulated or forced into servitude.
The Grysks, with the assistance of the telepathic Agbui, a client species of the Hegemony, delved into the minds and souls of potential clients. By exploiting their deepest fears, desires, hopes, and memories, the Grysks twisted them to their will, ultimately enslaving them. These "clients" then became willing to fight and die for their new masters. Additionally, the Grysks targeted what a species valued most, threatening it to force compliance. In cultures that blindly followed their leaders, the Grysks sometimes bypassed subversion and simply bent the existing government to their purposes. The Chiss ozyly-esehembo named Vah'nya believed that as few as three Grysks could control a nation, and one hundred could rule an entire world.
Thrawn emphasized that the Grysks were not to be underestimated, and any retreat should be viewed as a strategic choice. As a warlike species, the Grysks possessed a variety of starships, including elliptical vessels similar to Corona-class armed frigates, a type of long-range heavy freighter, a type of small transport, a type of spacetug, and a type of warship.

Grysk warriors employed a type of lightning gun and a type of pellet gun. Their armor and helmets featured curves on the left side and a distorted right side. Grysk weapons and armor were ritually disfigured on the right side, possibly reflecting the level of animosity towards the species they fought or the duration and intensity of the conflict. The damage appeared chronological, with older deformities showing more signs of wear. Thrawn believed that the trophy collection of a Grysk warrior group could represent the Grysks' overall military history and could help locate their homeworld. He also noted the existence of tales about some of the Grysks' wars.
Grysk warriors ingeniously replaced their teeth with upper and lower moldings containing break-apart weapons, communicators, and lock-breakers. This allowed them to communicate in their coded language using ultrasound signals through starship bulkheads, as demonstrated during a skirmish aboard the Chimaera.

Having surveyed the Empire, the Grysks were familiar with Imperial-class Star Destroyers, the capabilities and limitations of TIE starfighters, and other Imperial technology, which they used against Imperial forces. However, they had cultural blind spots, such as prioritizing the nearest enemy, which influenced their combat tactics. Despite their knowledge of Imperial weaponry, they were unprepared for the TIE/d "Defender" Multi-Role Starfighter during their encounter with the Chimaera, rendering them unable to effectively counter it.
Prior to the Battle of Atollon, the Grysks engaged in conquests within the Unknown Regions of the galaxy, leading to conflicts with the Chiss Ascendancy and other factions. Artistic memorials were created by survivors of these conquests. The Chiss Ascendancy maintained records of numerous battles against the Grysks, both those they participated in and those they observed. The Grysks, in turn, degraded the right side of their helmets and armor to commemorate past wars against various species and groups.
Despite their successful conquests, the Grysks considered the Chiss Ascendancy a significant threat requiring careful planning. Jixtus was placed in command of this campaign, believing that exploiting the Chiss's socio-political structure and strict non-interference policies was the key to their defeat.
Jixtus attempted to use the latter against the Chiss by employing the Nikardun Destiny, led by General Yiv the Benevolent, to conquer the worlds surrounding the Chiss Ascendancy, effectively trapping them in an unwinnable situation. However, Senior Captain Mitth'raw'nuruodo, who disregarded the Ascendancy's non-interference policies, uncovered Yiv's campaign while investigating suspicious attacks, thwarting his plans.
Despite Yiv's failure, Jixtus remained confident in his advantage over the Chiss and began manipulating their hierarchy by using the Agbui to spread a rumor about a planet, Hoxim, rich in valuable nyix alloy, a metal crucial for Chiss warships. He intended to incite a civil war among the Chiss families, whose socio-political system was constantly strained by rivalries and alliances. His plan nearly succeeded, with warships from the Xodlak, Pommrio, and Erighal families simultaneously approaching Hoxim to claim it. The resulting tensions threatened to erupt into a battle, but Thrawn intervened, preventing the fighting.
Despite Thrawn's intervention, tensions remained high. Jixtus, undeterred by his near failure at Hoxim, believed the Chiss were too fractured to defend themselves effectively. After spreading further rumors and misinformation to high-ranking Chiss military leaders, he launched a formal military campaign, enlisting the Kilji Illumine to bolster his fleet. However, Thrawn ultimately defeated him through superior tactics and alliances with former victims of Yiv's campaign, including the Paccosh, Garwians, and Vaks. Realizing his defeat, Jixtus detonated his own ship to prevent information about the Grysks from reaching the Chiss, killing himself in the process, but not before vowing that the Grysks would return. Despite exposing Jixtus's plot and saving the Chiss from destruction, Thrawn was exiled by the Ascendancy Defense Hierarchy Council for repeatedly violating Chiss non-interference laws, leading him to join the Empire. However, this was orchestrated by Thrawn, General Ba'kif, and Admiral Ar'alani to investigate the Empire as a potential ally against future Grysk invasions.
During the Clone Wars between the Galactic Republic and the Confederacy of Independent Systems, the Grysks monitored both sides. They later provided Count Dooku, the Head of State of the Confederacy, with information on cortosis, a lightsaber-resistant material. Dooku dispatched Duke Solha to Mokivj to mine cortosis and incorporate it into B2-series super battle droids. To the Grysks' surprise, the Mokivj droid factory also began producing clone trooper armor. Unbeknownst to the Grysks, Dooku, secretly the Sith apprentice Darth Sidious to Darth Sidious, who was publicly Supreme Chancellor Sheev Palpatine of the Republic, planned to add cortosis to clone armor to protect the clone troopers when they betrayed their Jedi Generals as part of Order 66. Ultimately, the mine was destroyed.
Shortly after the Battle of Atollon, a key event in the uprising rebellion against the Galactic Empire, the Imperial capital ship Chimaera traveled to Batuu to investigate a disturbance in the Force sensed by Emperor Palpatine. While the Chimaera was above Batuu, Sensor officer Commander Hammerly detected four small transports in loose formation above the planet, bringing the total number of starships on or above Batuu to ten. Commodore Karyn Faro and Hammerly attempted to identify the vessels, speculating that they could be small freighters or warships. As they gathered information, two more ships exited hyperspace 400,000 kilometers ahead of the Chimaera, identified by Hammerly as long-range heavy freighters.

The ships were heading directly for Batuu. Faro believed that all the unidentified vessels were destined for Black Spire Outpost, where Grand Admiral Thrawn and Darth Vader were conducting their investigation. Hammerly determined that the two new starships had arrived from the same hyperlane as the Chimaera. Shortly before a skirmish on Batuu between Thrawn, Vader, and a group of Darshi, one of the heavy freighters approached Thrawn and Vader's position, while the remaining vessels maintained orbit above Batuu. Vader ordered Commander Kimmund and his unit to intercept, examine, and engage the other heavy freighter.
Shortly after the skirmish, Kimmund and his stormtroopers approached the heavy freighter in the Darkhawk, but the Grysk vessel detected them and broke orbit. Defender Squadron One arrived and disabled the Grysk starship, preventing its escape and chasing away the smaller transports.
After the Chimaera's expedition, Grand Admiral Thrawn concluded that an invasion of the galaxy was imminent. He manipulated the Grysks into potentially attacking the Chiss Ascendancy before the Empire, believing they would continue to prioritize the nearest enemy. By 1 BBY, the Grysks had begun incursions into Imperial territory, committing various criminal acts, as noted by the Chiss Admiral Ar'alani.

The Grysks made their debut in Timothy Zahn's 2018 canon novel, Thrawn: Alliances. They bear a resemblance to the followers of alien warlord Nuso Esva, known as the Chosen, from Zahn's Star Wars Legends works. Like the Grysks, the Chosen could easily subjugate and force others to fight for them with unwavering dedication. Their leader, Nuso Esva, also concealed their identity, similar to Jixtus, and was defeated by the Quesoth, an insectoid species who turned against Esva after he killed their leader, the Queen of the Red, mirroring how the Kilji inflicted significant damage on Jixtus after he killed their ruler, Generalirius Nakirre.
Following the release of Thrawn: Alliances, Zahn confirmed his plans to further explore the Grysk threat to both the Chiss and the Empire, which he did in his subsequent works, Thrawn: Treason and the Star Wars: The Ascendancy Trilogy. The Grysks were first visually depicted in the third issue of the comic miniseries Star Wars: Thrawn: Alliances, an adaptation of the novel Thrawn: Alliances, with illustrations by Andrea Di Vito and Pat Olliffe.
In a French YouTube channel interview with La Tribune de Coruscant on May 5, 2023, Timothy Zahn stated that in his mind, the Grysks were the Far Outsiders mentioned in the 2006 novel Outbound Flight, due to the vagueness of the threat's description. However, this is not accurate, as Outbound Flight references the biotechnology of the Yuuzhan Vong, which the Grysks do not possess. Initially, Mitth'raw'nuruodo appeared dismissive of Kinman Doriana's description, even requesting proof of this threat from Darth Sidious. He later inquired whether Darth Sidious and Doriana had actually seen the invaders, to which they replied in the negative. Thrawn then confirmed that the Chiss had already engaged in a battle with the Yuuzhan Vong.