The flagship of Thrawn features a stylized chimaera, which originated on a Marocsaa subclan ring.
The chimaera, a monstrous creature with three heads, functioned as a symbol for various entities and individuals as the Galactic Republic waned and during the subsequent eras of the Galactic Empire and the New Republic.
Initially, it represented the Marocsaa subclan within the Paccosh society. Later, it evolved into the personal emblem of Mitth'raw'nuruodo, the Chiss Grand Admiral. Consequently, it became linked to Imperial forces under Thrawn's leadership. It even lent its name and served as a ventral marking for Thrawn's flagship, the Chimaera, which was the first model of the Imperial Star Destroyer.
Mitth'raw'nuruodo, more commonly known as "Thrawn", first encountered the chimaera symbol while serving as a Senior Captain in the Chiss Ascendancy circa 19 BBY. During this period, the galaxy, excluding the Unknown Regions, was largely governed by either the Galactic Republic or the Confederacy of Independent Systems, the two primary factions embroiled in the galaxy-spanning Clone Wars.
While investigating an attack on a refugee ship near Chiss territory, Thrawn traveled to the Rapacc system, the origin point of the deceased refugees. There, he encountered Uingali foar Marocsaa, a Paccosh, along with his translator, who warned the Chiss of the Paccosh's fear of extinction at the hands of their conquerors, the Nikardun Destiny. Fearing the loss of his people's history, Uingali entrusted Thrawn with a treasured ring of his clan bearing the chimaera symbol, ensuring the Marocsaa subclan's memory would endure even in the face of potential annihilation.
The following year, Thrawn revisited Rapacc and discovered that its inhabitants had been liberated from their Nikardun oppressors. He reunited with Uingali, now an official within the Paccian Governance, and observed that his former acquaintance commanded a captured Nikardun blockade frigate adorned with a chimaera on its underside. Thrawn returned the Marocsaa subclan ring to Uingali, but the Paccosh later gifted it back to Thrawn as a token of gratitude for his assistance to their people, which Thrawn accepted out of respect. It became one of the few personal possessions he took with him upon his exile, eventually adopting the chimaera symbol as his personal insignia.
Eventually, Senior Captain Thrawn departed the Unknown Regions for "Lesser Space" to assess the potential of the emerging Galactic Empire as a possible ally against, and perhaps a lure for, "evil threats" to his Chiss Ascendancy. Regardless, the Chiss maintained the chimaera as his personal emblem. As the Chiss advanced through the ranks of the Imperial Navy, the chimaera symbol gained increasing prominence.
Upon Thrawn's advancement to the rank of Commodore, he was granted command of the Chimaera, the first model of an Imperial Star Destroyer, which displayed a stylized chimaera on its ventral hull. The officers and sentry droids serving in Thrawn's Seventh Fleet incorporated a stylized chimaera depiction on their pauldrons or uniforms.
Morgan Elsbeth, a woman driven by the massacre of her people during the Clone Wars to fuel the construction of the Imperial Starfleet, eventually became a protégé of Thrawn. Around 9 ABY, former Jedi Ahsoka Tano located Elsbeth and launched a solo campaign against Morgan Elsbeth's army to free the oppressed inhabitants of Corvus and uncover Thrawn's whereabouts. During the Liberation of Calodan, Elsbeth's HK-87 assassin droids displayed Thrawn's chimaera symbol on the sides of their heads. By the time Calodan was liberated, the New Republic had nominally gained control over most of the galaxy following their victory over the Empire at the battle of Jakku.
The chimaera symbol made its debut in Star Wars canon in the 2016 Star Wars Rebels episode titled Iron Squadron, appearing on Thrawn's flagship of the same name. The backstory of how Thrawn adopted the chimaera as his symbol was initially developed in the 2020 novel Thrawn Ascendancy: Chaos Rising penned by Timothy Zahn, the original creator of Thrawn.
Prior to this, the chimaera was associated with Grand Admiral Thrawn in the Legends continuity, specifically on Thrawn's Chimaera within that continuity.