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They all crack sooner or later.
~ Jaco to Sarge about Pax.
Jaco is a supporting antagonist turned into a protagonist in Season 6 of the TV series Marvel's Agents of S.H.I.E.L.D. He is a mercenary and scientist as well as a member of a team led by Sarge in his quest to destroy the Shrike and kill their creator Izel.
He is portrayed by Winston James Francis.
In his past life on his own homeworld, Jaco had seven brothers and he was the mischievous one. He also had a close relationship with his youngest brother and taught him to bake as part of the family business. However, after the Shrike led by Izel invaded the planet and destroyed it along with everyone else, including Jaco's family, he was saved by Sarge and joined his team to prevent it from happening to other worlds.
Along the way, Jaco breathed through chemicals similar to his homeworld's atmosphere so he could keep his fire-breathing ability under control. At some point, the crew attempted to save Chronyca-2, homeworld of the Chronicoms, but were too late and forced to escape.
Arrival on Earth
When the Shrike arrived on Earth, Sarge sent his subordinates to make sure that the pathway was clear for him and his truck. As Jaco arrived, however, he witnessed his teammate Tinker crossing into a cement wall, killing him. He then reunited with Snowflake and Pax and told them about Tinker's death and that Sarge's path was blocked by a museum. The three succeed in destroying the museum and Sarge arrived without trouble despite the interference of S.H.I.E.L.D.
After robbing a convenient store for supplies, the four learn that Tinker had the crystals in his pocket when he turned into cement. Needing more, the four robbed a jewellery store and stole the crystals they had. During this time, he and Snow fought May but she was defeated when Sarge intervened. He and Sarge then tested the weapon with Earth's crystals and successfully uncovered where the Shrikes were located.
After some time, the team tracked down a man possessed by a Shrike and killed him. They then tracked down a man named Deke Shaw but he didn't behave like any other Shrike hosts. After S.H.I.E.L.D. arrived and saved Deke, Jaco was trapped in his Framework, confusing him. Jaco was then kept in S.H.I.E.L.D. custody but refused to talk.
During his time there, Jaco pretended to be sick as he didn't breathe his world's atmosphere. He then played dead before revealing his hidden ability to breathe fire so he could break out the crew. However, the agents caught on and subdued him. After Sarge struck a deal with S.H.I.E.L.D. director Alphonso Mackenzie, Jaco was brought onto the Zephyr before later being broke out by Sarge.
Defection and Sacrifice
After being motivated by Sarge's claim of Snow's death and the need to avenge her, Jaco and the other two took control of the Zephyr One. Jaco then witnesses Sarge execute Pax for slowing them down, becoming disgusted in what he did. After being inspired by Yo-Yo, Jaco betrayed Sarge and helped the team save FitzSimmons from Izel and the Shrike. He then sends the team off the ship while he lures the Shrike onto the ship and destroys them with Sarge's bomb.