WARNING: The following contains spoilers for Attack on Titan Season 4, Episode 19, "Two Brothers," now streaming on Funimation, Hulu, and Crunchyroll.
Possessing one of the Nine Titans to become a Titan Shifter is a great honor in the world of Attack on Titan. While some of the Titan Shifters have held their Titans from their introduction, a couple of Titans have changed hands once or twice, but none more so than the Jaw Titan. As of Season 4, Episode 19, "Two Brothers," Falco Grice is the fourth person to hold the Jaw Titan in AoT's main continuity. Marley has generally maintained control of the Nine, notably losing a few, but the Jaw is the only one they've lost and reacquired for now. Let's look back at everyone we know of who has possessed the Jaw Titan so far.
Marcel Galliard Was Originally Part of Reiner, Bertholdt, and Annie's Team
When Bertholdt Hoover's Colossal Titan first peeked over the Wall at the start of Attack on Titan, it was the beginning of the renewed war between Marley and Eldians. Along with Bertholdt's Colossal, Reiner's Armored, and Annie's Female, Marcel Galliard's Jaw Titan was chosen to carry out this operation. Marcel was a top cadet in Marley's Warrior training program and was chosen by the military to inherit the Jaw Titan. Marcel was the de facto leader for this mission whom Reiner began to emulate after Marcel's death.
Unlike the rest of Marley's Warrior program, Marcel didn't see inheriting one of the Nine as a gift, but as a curse. Marcel even sabotaged his own brother's attempt to inherit the Armored Titan to spare Porco from a short, violent life as one of Marley's Warriors. The day before they were meant to attack the Walls, a mindless Titan emerged from beneath their campsite and lunged at Reiner. Marcel shoved Reiner out of the way and was eaten by this mindless Titan which then escaped, marking the first Titan Marley had lost since the Great Titan War.
Ymir Never Intended to be a Titan Shifter
Reiner and Bertholdt were stunned to learn that Ymir was the human inside the Titan who had eaten Marcel in front of them. Ymir's real name is unknown, as she was named after the deity known as the Original Titan and worshipped as a goddess in a poor area of Marley. When she was discovered and turned into a mindless Titan, she was left to wander outside the Walls on Paradis Island for 60 years. After eating Marcel and becoming a human once more, she infiltrated the Walls as well and posed as a soldier, not to spy, but to survive.
Ymir eventually learned that her comrade Krista Lenz was actually Historia Reiss, a member of the Titan Royal Family, and initially intended to use the information to negotiate her safety from the wrath of Marley if they ever discovered she has stolen the Jaw Titan. After Reiner and Bertholdt were outed as spies and left to die in a Titan horde, Ymir helped them escape and turned herself over to them as a trophy to take back to Marley. Ymir decided she just wanted to return what she stole, and she was fed to one of Marley's Warrior Candidates.
Porco Galliard Just Wanted to Prove Himself
Porco Galliard, Marcel's younger brother whom he tried to spare from life as a Titan Shifter, inherited the Jaw Titan by consuming Ymir. Porco had been all but certain to be the one to inherit the Armored Titan, and he never knew that his brother had swayed Marley against him to protect him. Porco aimed his anger at Reiner, who he felt had never deserved to inherit one of the Nine. Porco was the least conflicted about his role as a Warrior of anyone, as he served Marley loyally during his time as the Jaw Titan.
Once war broke out in Shiganshina in Season 4 of Attack on Titan, Porco fought to steal the Founding Titan away from Eren, but instead was beaten almost literally to death by Eren's Attack Titan. After receiving a memory from Reiner of Marcel's confession that he had sabotaged Porco to protect him, Porco was moved by his brother's love and quite satisfied with proof that he was always better than Reiner. On death's door anyway, Porco refused to die for nothing and allowed a freshly-turned-Titan Falco to eat him, saving the young man's life and ensuring the Jaw Titan would stay with Marley.
Falco Grice Has a Difficult Road Ahead
Falco only ever wanted to inherit the Armored Titan in order to protect Gabi, much the same way Marcel had protected Porco. After accidentally ingesting Zeke's spinal fluid from tainted wine, Falco was unable to escape his fate as collateral damage in Zeke's and Eren's plans. Falco's brother, Colt, refused to leave his side when Zeke screamed and the explosion from Falco's transformation killed Colt instantly. Becoming the Jaw Titan was never the plan and now when Falco wakes, he will have to cope with the fact that he killed both Porco and his own brother, even though neither was really his fault.
