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Angel is a pale young man, with a lean, muscular body. He has messy, neck-length blond hair.
Angel is a prodigy craftsman in Shiganshina where he meets Maria Carlstead, and the two walk to the main gate to wait for the arrival of the Survey Corps. Before long Angel and Maria hear the sound of cannons and it is revealed that Angel designed the cannons atop the Walls, and that it would not be beyond his abilities to improve them. The Survey Corps' return is heralded by a Titan outside the Wall throwing heads of dead soldiers into the town, including the corpse of Heath Munsell. Angel is fascinated by the sound of the Titan walking away, remarking that a Titan must be far larger than a human, and becomes fascinated with the creatures.
When Angel returns to his workshop he finds he has been given a sample of a new material called iron bamboo. Not long after this Angel is called upon to journey to the newly constructed Industrial City with Xenophon Harkimo, Corina Ilmari, and Sorum Humé. While on their way the convoy falls under attack by militants. The soldiers are able to fend off the attack, but not before Angel and Xenophon are forced to fight. Upon arriving at the Industrial City, Angel learns of the existence of Iceburst Stone and collects samples of it. The next week is spent creating a Device that would allow humans to move in three dimensions.
When Angel returns to Shiganshina, he sees members of the Titan Cult opening Shiganshina's gate. During the confusion a single Titan enters the city. As it bears down on Angel and Corina Angel manages to dodge the Titans steps, but Corina is crushed. Angel watches as the Titan tears off Corina's pulverized head and eats her body. Enraged by this Angel jumps onto a wagon and begins to race toward the gate with the Titan in tow. As he exits the town and the gate shuts behind him Angel tests his device by firing a hook into the Wall and reeling himself onto its side. The rope, however, begins to fray, but luckily Maria sends down a ladder from the top of the Wall and pulls Angel to safety.
After refining his device Angel decides to go with Sorum on a Survey Corps expedition to attempt to kill a Titan. The Corps is able to capture a Titan successful, but when trying to kill it, they accidentally blow its restraints off. This forces the Corps into retreat. Mammon, the Titan that broke into Shiganshina, joins the first Titan and catches up with Angel and Sorum. Sorum jumps onto the Titan's head and detonates an explosive, allowing himself to be killed in order to destroy Mammon's nape. While Angel rides back to the Walls Angel mourns his friend, but he noticed that Mammon began to evaporate. Angel mistakenly deduces that the weak point of a Titan is the throat.
After they return, the Corps' further expeditions outside are put on indefinite hold, and the Corps itself is technically dissolved, and Angel begins obsessively working on his Device. The end result of the Device has the wearer use one hand to operate the Device's controls to the hooks, and hold his sword with the other. Angel attempts to persuade Jorge Pikale into exiting the Wall once more, and the commander agrees to an expedition if Angel can beat him in a fight. Angel attempts to fight using the equipment, and although he gains experience using his Device in combat, he loses to Jorge. The next day Angel tells Maria to open the gate briefly for him to exit the Walls and hunt a Titan. Maria agrees and the next day Angel waits at the gate with his horse when he sees Jorge and the rest of the Survey Corps, who have torn the Wings of Freedom off of their uniforms.
The group exits the gate and soon finds a Titan. Angel engages it with his Device and attacks its throat. When his slash fails to kill it Angel panics and gets caught behind its head. Angel realizes that the back of the neck was also destroyed in Sorum's blast. He tries to swipe its nape, but finds that with the single sword it is impossible to cut. Angel unhooks himself from his equipment and detonates the gas canisters, destroying the nape and killing the Titan. As Jorge picks him up and begins the journey back to the Walls, Angel remarks that he wishes that there was a way to add a second sword to the Device.
He was a master craftsman, and credited with creating multiple inventions that are still in use.
- "The Device" - A device allowing humans to make up the difference in height between a human and Titan, so that they can reach their weak point.
- Cannons - Heavy, strong weapons meant to sit upon the Walls to keep Titans at bay from inside the Walls. It is also implied that Angel is capable of rifling the barrels in order to increase range and accuracy.
- Iron bamboo Net - A strong net made from iron bamboo, meant to allow humans to capture Titans.
- Corina Ilmari - She was Angel's young assistant. When the Titan Mammon devoured her, Angel took it very hard. Her death fueled his attempts to find the Titans' weakness.
- Maria Carlstead - The two have been close friends since they were children. As they have gotten older, Maria has taken on more of a motherly role. Often fixing his hair, badgering him about cleanliness, and generally caring about his well being.
- His surname is Finnish, in which the word "aalto" means "a wave".
- Angel also invented the Cannons atop Wall Maria. It is unknown if he made the other cannons atop the other Walls.
- Angel is the second person to successfully kill a Titan, the first being Sorum Humé.
- However, while Sorum's kill was achieved mainly through luck, Angel was the first person to successfully locate and exploit a Titan's weak point.