"Big-Mouth" became the designation for a clone originating from the bounty hunter known as Jango Fett. As a clone corporal, he fought for the Grand Army of the Republic within the battalion commanded by Jedi General Depa Billaba. During the Battle on Haruun Kal, where Separatist General Grievous inflicted ninety percent casualties on the battalion, Big-Mouth was one of only four to survive. Alongside Commander Grey, Captain Styles, and Sergeant Soot, the other survivors, he joined Billaba's new battalion, which also included her Padawan, Caleb Dume, and clone trooper Stance.

One of the many clones derived from the bounty hunter Jango Fett, created on the planet Kamino for service as a clone trooper within the Grand Army of the Galactic Republic, adopted the moniker "Big-Mouth." During the Clone Wars, a conflict between the Republic and the Confederacy of Independent Systems, Big-Mouth, holding the rank of Clone Corporal, was under the command of Jedi General Depa Billaba. He fought alongside her on Haruun Kal against forces led by General Grievous, a cyborg who was the Supreme Commander of the Droid Army. Their battalion suffered a staggering ninety percent loss, with only four clone troopers from Billaba's unit surviving: Big-Mouth, Soot, Styles, and Grey. The Jedi herself sustained injuries so severe that she entered a coma.
Following a period of six months, Billaba regained consciousness and chose the youngling Caleb Dume as her Padawan apprentice. They were assigned a mission to scout the planet Kardoa for any Separatist presence, and Clone Commander Grey brought together her four surviving comrades, including Big-Mouth, who was a corporal at the time, to serve with her again. The commander also arranged for the veteran clones Lieutenant Remo and Corporals Mixx and Kaylon to be assigned to the battalion under Billaba's leadership, but the majority of the troopers were inexperienced recruits fresh from Kamino.
Grey shared this intelligence with the Jedi and her Padawan during a briefing at their camp on the surface of Kardoa. The next day, the operation commenced, with the Republic forces dividing into five squads to search the planet's canyons. Big-Mouth was assigned to Billaba's team, which also included Dume and the clone trooper CT-1157, one of the new recruits whom Big-Mouth kept a close eye on. As they moved, Dume and CT-1157 started joking about the close supervision they were under from Billaba and Big-Mouth, respectively, earning disapproving glances from the general and the corporal.

While the two were joking, Billaba's squad was ambushed by Separatist B1-series battle droids, and Billaba instructed Big-Mouth to contact the other squads and request air support. However, the corporal discovered that their signals were being jammed by the Separatists and informed the general that no assistance was available. Billaba then ordered Big-Mouth to stay with Dume and keep the battle droids engaged while she slipped away to locate the Separatist's command ship. The clone followed orders, but quickly noticed that Dume was fighting too far ahead of the Republic forces, leaving him vulnerable.
The corporal attempted to call the Padawan back, but he was too late. A series of blaster bolts struck Dume across the torso, knocking him to the ground. Ignoring Big-Mouth's orders to stay in cover, CT-1157 rushed out to defend his friend, destroying three droids approaching the incapacitated Padawan. Meanwhile, Billaba had located the Separatist shuttle and attacked it, causing the Separatist Colonel Coburn Sear to order a retreat off-world to prevent his forces from being stranded.

The battalion was next assigned to the war-ravaged world of Mygeeto, where they were tasked with clearing the Southern Mesas of Separatist forces during the Third Battle of Mygeeto. Before being assigned a squad to lead and departing for the mesas, Big-Mouth gave Dume one of his signature meiloorun fruits. While he and his men were in the field, Billaba, Grey, Styles, Dume, and CT-1157, now known as Stance, returned to their camp after being rescued from battle droids by the Mandalorian Skull Squadron, only to be attacked again, this time by Grievous and Sear.
Big-Mouth and the other clones were summoned back for support, but before they arrived, Sear managed to kill Stance, only to be killed himself by Dume in retaliation. Billaba sustained injuries while fighting Grievous but managed to hold him off until the reinforcements arrived, forcing him to retreat. Following the battle, a burial service was held for Stance, and then the clones and Dume visited Billaba as she recovered in a bacta tank. Orders then arrived for the battalion to proceed to the planet Kaller as soon as the general was fit for duty.
On Kaller, the Republic forces engaged Separatist forces under the command of General Kleeve outside Plateau City, eventually routing them as they approached the city walls. Kleeve and the remaining Separatist forces fled the planet, and after meeting with the Kalleran Gamut Key in Plateau City, Billaba instructed her men to establish camp for the night in the fields outside the city walls. After Grievous ordered a major offensive, the Kaller system was targeted again, and Billaba's battalion once again fought battle droids, receiving assistance from Clone Force 99. However, during the fighting, the battalion received Order 66, and Billaba was executed by soldiers who had served with her for years.

Being a clone of Jango Fett, Big-Mouth's physical attributes included a height of 1.83 meters, tan skin, brown [eyes](/article/eye], and black hair. By the time he was stationed on Kardoa, he sported a prominent beard, which, unlike his hair, was gray. Big-Mouth was known for his constant consumption of meilooruns, often sharing them with his comrades and managing to find them even on planets where they weren't naturally available. He was critical of the lack of experience among many of the clones in Billaba's battalion on Kardoa, believing they required more training before being deployed. Consequently, he kept a close watch on one such clone, CT-1157, during their deployment.
Big-Mouth initially teased Dume for his relative inexperience, but when the Padawan took offense, the clone clarified that he meant no harm and offered the boy some of his meiloorun. After witnessing Dume's eagerness in battle during the initial fighting on Kaldoa, the corporal complimented the boy's performance but later unsuccessfully attempted to prevent him from being shot down while fighting too far from his own troops. Big-Mouth and Dume developed a bond while fighting together on Kardoa, and afterwards, he frequently offered him meilooruns.
During the battle of Kardoa, Big-Mouth wore Phase II clone trooper armor with green markings on the helmet and carried a DC-15A blaster carbine.

The character of Big-Mouth was conceived by writer Greg Weisman and illustrator Pepe Larraz for the Star Wars: Kanan series of comic books, making his debut in the second issue on May 6, 2015. His initial appearance in Kanan 2 depicted his death, but subsequent issues of the comic explored Big-Mouth's earlier exploits in the Clone Wars before Order 66, including his growing friendship with Caleb Dume.
However, the Star Wars: The Bad Batch episode "Aftermath" presented a different depiction of Order 66 on Kaller, with no mention of Big-Mouth. Given its more recent release, this article assumes "Aftermath" is the accurate account. In Kanan 2, after nightfall, the clones gathered around campfires in the fields, with Billaba sitting with Dume, Styles, and Grey. As they celebrated their victory over Kleeve, they received a communication from Supreme Chancellor Sheev Palpatine, issuing Order 66, a directive to eliminate all members of the Jedi Order. Despite their friendship with Dume and Billaba, the clones were compelled to comply due to inhibitor chips implanted in them by the Kaminoans under Palpatine's orders. Big-Mouth and the rest of the battalion opened fire on the general and the Padawan, with Billaba killing Kaylon, Remo, and Mixx before Dume could react. The boy then used his lightsaber to deflect blaster bolts back at Big-Mouth and Soot, killing them both. Styles and Grey then killed Billaba, but Dume escaped the clones and went into hiding.