Gwendal is a tall and handsome man with long dark grey hair, tied in a ponytail whereas he has fringes on the sides of his face, and deep blue eyes. He is usually seen with a stern face and a wrinkled forehead that he people often point out.
In the anime, he's often seen wearing a white dress shirt underneath a green military coat with a brown belt, where his scabbard and sword is placed on his left hip. In the manga, he seems to wear a fancier version of his coat adorned with a cravat, although the cravat seems to disappear from time to time.
He is a no-nonsense type of person that considers the well being of the country among everything else. He is usually seen with a stern face, but he actually likes adorable things and does knitting as a hobby.
He is also shown to have a soft spot to his relatives, of as shown when he decides to send away his cousin, Gegenhuber, to find the Mateki instead of executing him for his heavy sin. While he does not outwardly show much affection towards his brothers, he shows in times of great stress that he does care.
Gwendal is a tough guy except when it comes to his childhood friend, Anissina, and arguably his family. He is afraid of Anissina and often hides from her so he can prevent being used in one of her crazy experiments. He is even seen sweating in panic at the thought of her.
In the manga, he is portrayed to be more heartless and sharp-tongued, especially during the early chapters. When Yuuri first came, Gwendal was quick to voice out his disapproval once he heard that Yuuri "never wanted to be king". Despite that, he remained faithful to Shinou's wishes and accepted Yuuri as Maou when he finally took on the position. He was eager enough to protect the Maou, especially during their journey in Svelera.
Despite his not-so-good first impression, he is still subjected to be stuck in certain situations and react comically, like when he vacated his seat during an important meeting just to take care of abandoned kittens in the rain. He is even nicknamed to be the "Foster Father of Small Animals in Shin Makoku", which later on became "Lord Gwendal "Hardship Bearer" von Voltaire".
Gwendal is the current head of the Voltaire house, and is one of the Ten Aristocrats of Shin Makoku. He is a well-rounded soldier, who is skilled in swordsmanship and battle tactics. He is a good leader, and most often keeps the country in check when the Maou is not around.
When not otherwise busy, Gwendal indulges in his hobby of knitting but often the creatures he makes look nothing like what they're supposed to (for example a bear got mistaken for a black pig or a cat that looks like a raccoon).
He is fond of cute animals or objects such as the dolphin key chain (Bandou-kun) Yuuri received at the dolphin show, which was later on passed to Gwendal. When they returned to Shin Makoku, Gwendal gave Yuuri a little kitty keychain although Yuuri had mistaken it for a raccoon.
Ever since they were children, Anissina always sought out Gwendal so she could test out her inventions that needed test subjects. Most of it were failures, and Gwendal mostly suffered from its aftermath. On the bright side, Gwendal learned how to knit because of Anissina. He is adamant that knitting helps him sharpen his concentration, but it is actually just a stress reliever.
Gwendal's uncle, Stuffel staged a coup by kidnapping Yuuri. Gwendal is prepared to start a civil war, but Conrad saves Yuuri in time, and he interrupts the battle. The Maou surfaces and gives Günter the opening to arrest Stuffel.
When he and Yuuri were alone in the desert following a sand trap that sucked in Wolfram and Conrad, Gwendal showed certain care he tried to hide towards Yuuri. It was at that time Yuuri later commented to Conrad that all of the siblings have similar kind smiles. Later on, it was revealed that Gwendal's left eye is the key to one of the four forbidden boxes, the "End of the Earth". When the "key" was taken from him, he cannot see from his left eye.
When he was younger, Gwendal despised humans, a habit called the Mazoku pride by Dunheely Weller. On Dunheely's last journey to a nameless village, he told Gwendal to enjoy the ride before their last duel. Upon arriving in the village, Gwendal is shocked that the village isn't recognized by Shin Makoku, and leads the attack on the bandits which targeted the village.
In this duel, Gwendal sees Dunheely for who he really was, an old man, not the agile man he knew when he was younger.
Dunheely later dies of old age, and Gwendal buries him near the tree where Dunheely told Gwendal what he was looking for. Years later while on a picnic with his family and Yuuri, Gwendal admits that Dunheely was a larger existence than anyone else within him, because he hated that man.
- His hobby is knitting stuffed animals and he claims that it helps him to concentrate.
- His most precious item are his collection of stuffed animals.
- He's bothered when people points out that the wrinkles between his forehead are getting more visible.
- Anissina was the one that taught him how to knit.
- Kyou Kara Maou, Episode 12