Theseus Scamander? The war hero?
-- Momolu Wotorson (WFT)
Theseus Scamander was the older brother of Newt Scamander, a well-known hero of World War One, and an Auror for the Ministry of Magic in the 1920s.
When Newt Scamander appeared before MACUSA in 1926 after creatures escaped from his case, the British Envoy recognized his last name, as did a witch named Momolu Wotorson, because of his famous elder brother Theseus (WFT).
The more peace-loving Newt believed his brother was wrong to use violent “ends to justify the means” as an Auror (CG).
In 1927, Newt saw Theseus again at the Ministry of Magic when he attended a hearing about having his traveling privileges restored, but the group of Aurors who heard his plea reminded him that his creatures went on a rampage in New York, and that he consorted with violent Obscurial, Credence Barebone. Theseus told Newt that Credence was still alive and asked his help in hunting him down, which made Newt walk out of the hearing because he did not want to choose sides or possibly have to kill Credence (CG).
However, when Newt eventually traveled to Paris illegally with no-Maj Jacob Kowalski to hunt down the Goldstein sisters, his path crossed several times with Theseus in confrontations with Gellert Grindelwald. Newt also disguised himself as Theseus via Polyjuice Potion when he and Tina went to the French Ministry to find records about Credence and his true identity. When the potion wore off, Theseus saw Newt and chased him, but was bound and slammed into a wall by Tina, which Newt described as “the best moment of my life” (CG).
Dumbledore had warned Theseus not to try and break up any of Grindelwald’s rallies if ordered to by the Head of Magical Law Enforcement Travers. When they arrived at the scene of one rally in the Pere Lachaise Cemetery, Theseus showed leadership in telling the other Aurors, “Use minimum force on the crowd,” and “Do nothing. No force.” But when a young hot-headed Auror accidentally killed a follower of Grindelwald anyway, Theseus knew he had no choice and ordered “Let’s take him.” Grindelwald surrounded himself with a ring of black fire and dared the Aurors to cross the line and join him. He also reached out to Theseus’s fiance, Leta Lestrange, who suddenly sacrificed her own life in the fire to save both Newt and Theseus, allowing them to disapparate away from Grindelwald.
Brother to magizoologist Newt Scamander. Engaged for a time to Leta Lestrange.
The magical world on both sides of the Atlantic considered him a hero of World War One. He tried to use calm leadership to control the other Aurors in their confrontations with Grindelwald in the 1920s.
Theseus was a famous mythical Greek hero and founder of ancient Athens.
Actor Colin Farrell who played Percival Graves revealed in an Interview with Snitchseeker that his character was acquainted with Newt through his war-hero brother. Farrell said he was told that Theseus was a "very powerful and commanding British Auror." The text of the script, however, just calls him a war hero, not an Auror. Another possible clue to this is a letter designed by MinaLima for the first Fantastic Beasts movie in which Theseus writes to Newt that he has been chosen by the Ministry to help hunt down Grindelwald, but it does not specifically label him an Auror. Note: This was cleared up in the second Fantastic Beasts movie, Crimes of Grindelwald, when Newt tells Spielman, "Theseus is the Auror. I think my talents lie elsewhere." ~ JK
Theseus' wand had a tortoise shell handle according to designer Molly Sole - Fantastic Beasts: The Crimes of Grindelwald: Movie Magic by Jody Revenson