Simmix, a male Fillithar who achieved the rank of Jedi Master within the Jedi Order, lived during the High Republic Era. He mentored Cohmac Vitus, his Padawan, who held Simmix in high regard as a kind instructor. Simmix joined Vitus, Master Laret Soveral, and her Padawan, Orla Jareni, in responding to the kidnapping of monarchs representing the planets of Eiram and E'ronoh. Due to a carefully planned trap by the Directorate, the criminal group responsible for the abductions, Simmix met his death when their T-1 shuttle crashed on the lost moon.
Vitus was deeply saddened by Simmix's passing, leading him to question the Jedi teachings regarding the management of emotions. Vitus committed to suppressing his sorrow and honoring Simmix through his dedication to the Jedi Order, but the loss of his master continued to weigh heavily on him for years afterward.
During the High Republic Era, Simmix served as a member of the Jedi Order as a Jedi. He eventually rose to the position of Jedi Master, and took Cohmac Vitus on as his Padawan. While training Vitus, who was prone to daydreaming, Simmix frequently reminded him to focus on being present in the moment.
In the year 257 BBY, the planets Eiram and [E'ronoh](/article/e%27ronoh], which are twin planets, requested assistance from the Jedi after their rulers—Queen Thandeka of Eiram and Monarch Cassel of E'ronoh—were taken as hostages by the Directorate criminal organization. Simmix and Vitus, along with Master Laret Soveral and her Padawan, Orla Jareni, were sent aboard a T-1 shuttle to offer their aid. Upon entering the shuttle, the Jedi noticed that the safety equipment was not designed for limbless beings like Simmix, but the Jedi Master dismissed the issue with a laugh, saying he would take the risk.
Simmix instructed Vitus to study the local legends during their trip, noting the importance of serpents in their stories. Vitus, unconvinced of its relevance, only briefly reviewed the material. While on the shuttle, Masters Simmix and Soveral engaged in meditation while Jareni and Vitus took on the role of pilots for the starship. After arriving in the Eiram system, their T-1 shuttle picked up a distress signal originating from Monarch Cassel's damaged vessel on the lost moon, a wandering moon located between the two planets. While the Padawans intended to investigate the signal, it turned out to be a trap set by the Directorate, leading to their shuttle crashing on the moon. Due to the shuttle's safety harness design, Simmix was killed in the accident.
After the crash, Master Soveral found Simmix's body. When Vitus regained consciousness, he reached out through the Force but could not sense his master, leading Soveral to confirm Simmix's passing with an apology. Vitus knelt by Simmix's body, closing his master's eyes. In the immediate aftermath of Simmix's death, Vitus was overcome with grief, blaming himself for not reminding his master of the potential dangers when boarding the shuttle. The three survivors were compelled to leave the wreckage, leaving Simmix's body behind. Soveral expressed regret but hoped the Directorate would assume he had traveled alone if they found him. After entering a cave system on the moon, Vitus recognized carvings of a serpent from the folklore and was later forced to battle several of the creatures that the carvings had warned about, haunted by the resemblence between the snakes and Simmix.
Jedi teachings suggested that Vitus should not grieve Simmix's death, as his master had become one with the Force; however, Vitus was angered by the expectation that he should not have formed an attachment after developing such a close relationship with his master. Vitus decided that showing his anger would provide no help, intending to serve the Jedi well in honor of Simmix. Despite this, Vitus was later envious when he witnessed Thandeka mourn the death of Cassel, knowing he could not acknowledge his own loss. Vitus buried his grief, believing that was what Simmix would have told him to do. Nevertheless, the loss of his master continued to deeply affect Vitus long after Simmix's death, and he remained doubtful of the Jedi teachings regarding the handling of emotions. Twenty-five years later, while Vitus—by then a Jedi Master himself—and several others, including Jareni, were stranded aboard the Amaxine space station following the Great Hyperspace Disaster, Vitus recalled Simmix after the supposed death of Jedi Knight Dez Rydan.
Simmix, being a Fillithar, had green scales. As a Jedi Master, Simmix was deeply committed to the Jedi Order and showed kindness towards his Padawan. While he was always careful with the lives of others, he often disregarded his own safety. His Padawan frequently pointed out his recklessness, which pleased Simmix, who joked that he had delegated his self-preservation to Vitus. Simmix believed that disagreeing with the Jedi Council was acceptable, and the important thing was how that disagreement was expressed.
Being a Jedi, Simmix possessed Force-sensitivity. Vitus perceived Simmix's presence in the Force as radiating a sense of calm and powerful centeredness.
Simmix, created for the Star Wars: The High Republic project, was first introduced—though only as a corpse in a flashback—in the novel The High Republic: Into the Dark, penned by Claudia Gray and released on February 2, 2021. His name was revealed in an excerpt from the novel within The High Republic Free Digital Sampler, which came out in 2020.
The second episode of Star Wars: The High Republic Show, which aired on March 29, 2021, depicted Simmix as a silhouette during a summary of the project's events. However, the silhouette portrayed Simmix as a humanoid figure with visible limbs, despite Into the Dark explicitly stating he was a limbless Fillithar. The episode also showed Simmix wielding a blue lightsaber and wearing Jedi robes.
In The High Republic: Tears of the Nameless, Simmix's scales are described as red fading to pink, while Into the Dark previously described them as green.