Rod was a rather short, overweight man, with a round face, short, jagged black hair and a thin black mustache. He was typically seen wearing the clothes of a wealthy man, featuring a white button-front shirt with a black pullover vest, loose black pants and black dress shoes.
In this form, Rod was an abnormal Titan. His appearance as a Titan retains practically nothing of his human form, except for still being male-like as most Titans are. He grows to the point of becoming the largest Titan ever known. However, his body was quite disproportionate, having a large torso with a small head, and very thin limbs for his size, thus being unable to stand up and needing to crawl on all fours. He was also notably skeletal, with most of his bones clearly visible and lacking in muscles, as well as his face and internal organs being exposed when he stood up in the wall.
Like the Colossal Titan, his enormous size causes him to move slowly and generate lots of heat, always being covered by clouds of steam. The heat he produces was so high that it was impossible to go near him without getting burned, and causes objects around him to spontaneously combust.
Rod often appeared to have a calm, yet slightly worried demeanor. He spoke with great certainty and intelligence about the events of his daughter, Frieda Reiss, and his brother Uri Reiss, when they obtained and lost the Founding Titan. Rod maintained a level head throughout most of his time with Historia, Eren Jaeger and Kenny Ackermann. He even gathered his composure after Kenny grabbed him and began shoving a knife down his throat. However, when Historia crushed the serum, threw him, and bashed his claims of godhood, he became erratic and panicked. After the syringe was shattered on the ground, he began lightly crying and desperately licked it off the floor so that he could become a Titan himself.
Rod was the eldest son of Mr. Reiss, the inheritor of the Founding Titan and the true king of humanity. Some time later, he was joined by a younger brother, Uri. Uri and Rod constantly begged their father to release humanity from their encagement, but he always refused, never disclosing why. It apparently had been so many times that Rod was locked behind bars for his attempts, and it is implied to have happened more than once. When it came time for his father to pass his position to a son, Uri volunteered, asking Rod to pray. After Rod observed his father's presence in Uri the moment his brother had opened his eyes, he realized he had become an all-knowing being and protector of the world; God. On his brother's promise, Rod had devoted his time to protecting God and offering his prayers to it.
As a young man, Rod married an unnamed woman and had five children with her: Frieda, Ulklin, Dirk, Abel, and Florian. Secretly, Rod conceived a sixth child, Historia, with Alma, one of his maids and confidant. When it was discovered, his mistress and daughter were exiled to a farm that he leased to Historia's maternal grandparents.
In the year 842, Frieda devoured Uri and became queen of humanity. However, just like Uri, Frieda fell to the influence of the First King, despite previously promising Rod that she would destroy all the Titans.
On the day of Wall Maria's fall, the entire Reiss family goes to the family's chapel to pray in its underground cavern. However, Grisha Jaeger breaks into the chapel to steal the Founding Titan, and Frieda is forced to engage him. Despite Frieda's immense power, she is defeated due to inexperience and is eaten. Grisha then slaughters the entire royal family, with only Rod surviving.
Several days after the fall of Wall Maria, Rod arrives to Historia's home, informing her that she would be living with him from now on. Kenny Ackermann and the Military Police First Interior Squad intervene, swarming around Historia and her mother. Kenny questions if Rod is familiar with the two women, which he denies. Kenny kills Alma, but as he prepares to kill Historia, Rod stops him and gives Historia the alias "Christa Lenz" to live by so that she will not have to die.
At Rod's suggestion, the royal government begins giving out food rations to the Walls' citizens, expending 60% of the government's food reserves. Despite other lords' misgivings, Rod insists that the expenditure was necessary to boost the citizens' morale, and to improve the royal family's public approval.
Rod and Kenny's squad take Historia and Eren to the cavern underneath the Reiss chapel, where he has Eren restrained so that the boy will not be able to transform. He also explains his situation to Historia, convincing her that any actions he has taken have only been taken with humanity's best interests in mind.
After Eren awakes, Rod observes that he seems to recognize the cavern despite never having visited it, noting that he is not surprised by this fact. Historia asks him to explain what is going on to Eren, but Rod instead has her place her hand on Eren, along with his own, to try to channel Grisha Jaeger's memories in Eren. After triggering the memories, Rod asks Eren if he has remembered his father's sin.
He notices that Historia is also visibly shaken, and is surprised to learn that the contact has also restored her memories of Frieda, who had visited her when she was young. He explains that Frieda was Historia's half-sister, and that Frieda likely erased Historia's memories of her to protect her. Historia asks to see Frieda so she can thank her, but Rod informs her that Frieda is dead, killed along with the rest of Rod's family by Eren's father.
They are interrupted by Kenny, who arrives to inform Rod that the military has successfully led a coup against the royal government, and that it is only a matter of time before they arrive at the chapel. Rod orders Kenny to take his squad and guard the entrance to the cavern, as he needs them absent for the ceremony.
After Kenny leaves, Rod retrieves a bag with a Titan injection in it, and tells Historia that there is a way for her to see Frieda again. Hearing the ruckus as Kenny and Levi's squads engage each other, Rod tells Historia that they need to hurry. Eren tries frantically to communicate with her through his gag since he knows what the syringe means for her, but she does not understand why he is so upset.
Rod tells her that is it because Eren knows that they intend to return the power his father stole to its rightful place, inside her. Rod explains the history of the Founding Titan, and the powers that it holds. He explains that Frieda would have been able to use the power to rid the world of the Titans, but that in the hands of a non-Reiss like Eren, the power is dormant.
Rod's monologue is interrupted by Kenny, who demands confirmation that the Founding Titan is useless to anyone who is not a Reiss. Rod confirms this, and Kenny grabs him and begins to threaten him, outraged that Rod has taken advantage of him. Rod is unfazed by Kenny's threats, simply saying that he is thankful for Kenny's service, and for Uri's decision to employ a "stray dog" such as him.
Kenny grows even more incensed at Rod's mention of Rod's brother, and threatens to kill Rod if he continues to bad mouth Uri. When Historia tries to stand up for her father, Kenny accuses Rod of only caring about Historia's royal blood, rather than Historia herself, and claims that Rod is a coward who is too afraid to become a Titan himself. Rod offers no argument, simply insisting that he cannot become a Titan himself.
Kenny finally releases Rod, and Rod frees Kenny from his service, suggesting that the man leave and live a long life on his own. However, to Rod's horror, Kenny approaches Eren and cuts the boy's head open, intending to force Eren and Historia to fight in their Titan forms for the Founding Titan. Rod panics and forces the syringe into Historia's hands, explaining that the injection will turn her into a Titan powerful enough to defeat Eren.
Historia hesitates, asking her father why none of the previous Founding Titans used their powers to help humanity, and Rod explains that it was the wish of the first Reiss King that humanity be controlled by the Titans, believing that it was the only path to peace. He does not know the reason itself because it is only known to those who inherit the world's memories. Historia knocks away the syringe, smashing it on the floor, to Rod's horror. He lunges at Historia, but she flips him over her shoulder, slamming him into the ground and breaking his back. As she goes to free Eren, Rod pulls himself across the floor to the shattered syringe, and laps up the contents of the syringe, transforming himself into a Pure Titan.
Rod's Titan then proceeds to ignore the Scout Regiment members underneath the Reiss Chapel and begins crawling towards Orvud District of Wall Sina, drawn to it by the city's large populace. The Scouts try to intercept him and lead him away, but are unable to get close to him because of the enormous amount of heat emanating from his body. He arrives at Orvud at dawn, where a group of Garrison and Scout Regiment members are waiting for him.
He arrives there at dawn, where the scouts and the Garrison are waiting for him atop the wall. The Garrison fires an enormous barrage of cannon fire at Rod, both from the Walls and from the ground. The cannons cause great damage on his back, but he withstands all the attacks and scales the Wall. The intense heat of his body and the wind change forces the soldiers to cover themselves in water to prevent them from being burned. His hands are blown off by Squad Levi, which makes him lose balance and fall over the Wall. After this, Eren shoves barrels of gunpowder into Rod's mouth, making an enormous explosion and blowing off his head and nape. To kill Rod's Titan once and for all, Squad Levi begins to cut up the flying pieces of its body in hopes of cutting the nape. Eventually, the piece of his nape is found and cut by Historia, who receives some of his memories in the process, one of which being Rod asking his father to release them from the Titans rule.
- Historia Reiss - Rod was Historia's father, though she is an illegitimate child who is not accepted as a suitable heir to the Reiss family. Thus Kenny Ackermann was charged with her death and the death of Historia's mother. Rod came to get her to live with him, but the Military Police interfered and rather than take back his daughter, Rod was forced to propose an alternative where his daughter's chances of survival would be extremely low rather than see his daughter's death before his eyes. It was thus implied that Rod Reiss may have cared for his daughter. When Eren and Historia were captured, Rod Reiss embraced Historia with tears in his eyes, saying that he was sorry for what has happened, surprising Eren and Historia. The reason for this, may have been his intentions for one day giving Historia the power of her half-sister. However, Historia refused to comply with his wishes that she become a Titan and eat Eren, realizing that the power destroyed her sister's humanity and that Rod was only using her to get the Founding Titan and regain the power of the Reiss family.
- Frieda Reiss - It was implied that Rod loved his daughter over all things. When Historia rejected the serum, he became furious because of the loss of Frieda's memories and power, and when he licked the serum, he said that he will be reunited with his family and with her.
- Alma - At first Alma was Rod's servant but eventually she became his confidante and lover. When she became pregnant, she was taken away to her parents' farm. Rod thought that she was the only person that could understand what he was going through.
- Rod Reiss' Pure Titan is the largest Titan in the series.
- When Rod's Titan was slain by Historia Reiss, she somehow saw some of his memories. It is unclear how that was possible without either of them having the Power of the Titans.
- Young Rod shares an English voice actor with Boris Feulner.