Yukimura based the fictional character on Thorfinn Karlsefni, as a soldier who initially commits horrible acts as a Viking but grows up to be more caring in later chapters, trying to understand other people and redeem himself.

[9] The final story arc was heavily based on real life events as Thorfinn meets the natives of Vinland: the Mi'kmaq.

[14] Thorfinn's quest for Vinland comes from Yukimura's interest in how the people of Northern Europe reached the Americas more than 400 years earlier than Christopher Columbus' discovery.

Yukimura's thoughts about the Cold War and the September 11 attacks were projected on Thorfinn's character, who is traumatized by his actions as a Viking and thus decides to find Vinland in order to make a land where people from different races are able to live together peacefully.

Thorfinn was written to be an ideal hero, something that Yukimura finds it hard to write but believes it is his job as a write to give his readers such protagonist[1] Once the series' fourth story arc started, Yukimura reflected on Thorfinn, telling a friend that the protagonist highlights how people can change in contrast to others, such as Thorkell, who do not want to effect such change.

She heard that she was to play an innocent child, so when she glanced at the script, she was shocked when told of Thofinn's threatening death despite his young age.

[28] Askeladd kills Sweyn during an audience, when the king announces his plan to invade Wales, feigning madness, so that prince Canute could rule the Danish-occupied parts of England without question.

[32] With Einar's help, along with Snake, the farm's head of security, and Ketil's father Sverker, Thorfinn learns to let go of his dark past and pursues a life of peace, away from the Vikings' violence.

[36][37] In order to gain the funding for the trip to Vinland, Thorfinn's group plans to travel to Greece and sell Narwhal horns there.

As tensions rise between the settlers and the natives and the fear of war between the two factions escalates, Thorfinn begins considering the possibility of leaving Vinland in order to protect the peace.

[51] The anime's second season added more content about Thorfinn's sins, in the form of nightmares where his past persona commits murders; and, as soon as he enters into a house of his victims, he is replaced by his slave persona who is in shock upon seeing the murdered victims, due to the realization of his sins, which was praised by Yukimura for how well the MAPPA studio understood Thorfinn's mind.

[53] Early response to Thorfinn's character focused on his tragic characterization, with Anime News Network noting his change of personality once his father is killed by Askeladd.

[59][60][61][62] In a more negative review, Anime UK News criticized the early characterization of Thorfinn for his dark traits, such as his moody stares or angst.

Polygon further praised the relationship between Thorfinn and Askeladd, as the former sees him as both his greatest enemy and a father figure, due to the time they spend together.

[64] The ending of the first season of the anime led to praise from the media in regard to how the writers handled Thorfinn's character arc as he questions his own revenge when Askeladd sees him sympathetically during his last moments.

According to the writer, while Thorfinn is originally driven by revenge, the manga also explores his desire to have power similar to "those who desperately struggle to find their homelands in the 21st century 'medieval' Japan".

[69][70][71] The Daily Star agreed and found that Thorfinn's mundane life as a slave brings intriguing stories about "redemption and self-discovery" even if it was imperfect.

[72] Anime News Network said that, when Thorfinn's innocence is lost following Thors' death, he becomes a flat character throughout most of the first story and the second, until Einar convinces him to enjoy his life despite their sadness.

[74][75] The Escapist Magazine said that while Thorfinn became "empty" with Askeladd's game as a theme of the revenge the anime had been exploring, his relationship with Einar helped to bring back his humanity.

[78] Comic Book Resources said the series' focus on violence was a charade after all and it was instead seeking freedom and Thorfinn counters Canute's ideals by searching for Vinland which the King cannot find or reach.

[79] In following arcs, Comic Book Resources similarly said that the series' audience will be surprised to see him turn into a pacifist soldier but that he still has problem interacting with other people to the point where he fails to start a romantic relationship with women interested in him.

[2] Sportskeeda noted that Thorfinn's becoming a pacifist is highly notable in how it changes his characterization to the point of calling it one of the most interesting from seinen manga,[80] with Polygon comparing him to Shigeo Kageyama and Naruto Uzumaki's alternatives options besides violence to end conflicts; In particular, Thorfinn's new wisdom when learning about Christianity and telling Canute's army "I have no enemies" were one of the biggest highlights of the anime as a result of redefining himself rather than going back to his Viking roots.

[81][82] Manga News comments that Thorfinn's pacifism is challenged as the sins he committed in his childhood are highlighted and he still fights, but avoiding casualties, making a major departure from the series' first chapters.

[84][85] Anime News Network said that, while Thorfinn's and Eren's origin stories are similar, they differ due to the latter's pessimistic tone, which contrasts the former's desire to grow up and live atoning for his sins in regard to how they change their outlook on war.

Eventually, Isayama felt that the slave arc allowed Thorfinn to define himself as a character and become more likable, due to how he accepts having committed too many sins and wants to redeem himself.

[97] In 2023, Yukimura recalled receiving several negative responses from fans after the ending of the first story arc, as Thorfinn is no longer portrayed as a Viking and instead spends his time farming.

[98] Following the ending of the second story arc of the series, Yukimura was surprised by the sudden rise of popularity of Thorfinn, especially within Western fans, when the protagonist tells Canute's army "I have no enemies".

[100] In another article, Beckett listed the scene where Thorfinn confronts Canute's soldiers as the best one from 2023 due to how he finally understood his father's lesson about what was being a warrior.

[102] The fights between Thorfinn and Thorkell were found by ComicWorthReading to be ridiculously superheroic, as a result of the character's movements, with DualShockers listing both as among those from the first season.

[103][104] Writer Hiroshi Seko believes Thorfinn's age and role in a story of Vikings to be one of the best reasons for the series' popularity.