Question: Severus Snape becomes a double-agent for an order that was founded by whom?

Context articles: The Melody Lingers On (film)
Severus Snape
Aurelia (gens)
Severus Snape and the Marauders
Potions in Harry Potter
John Nettleship
Alan Rickman
Cassius Severus
Order of the Phoenix (fictional organisation)
Marcus Silius Messala

A piano virtuoso has a child out of wedlock to her fiance, who is killed trying to save her life.
 Their son is brought up by foster parents and becomes a musician.
"In 1917, Carlo Salvini (George F. Houston), an opera singer and captain in the Italian army, returns home to participate in a performance of "Carmen" for a Red Cross benefit.
 Afterward, Carlo meets Franceska Manzoni (Helen Westley) and her niece, pianist Ann Prescott (Josephine Hutchinson).
 When German troops move closer to the village, Carlo and his fellow soldiers help Franceska, Ann and the other villagers evacuate.
 Before Carlo can get away, however, the German troops invade and Ann hides him in the attic.
 During the ensuing months, Ann and Carlo fall in love and marry.
 Carlo returns to the front line, and later Ann gives birth to their son, whom she names Carlo.
 Then, Franceska, who was her piano instructor too, dies, and her final wish is for Ann to dedicate young Carlo's life to music.
 In order to save her baby from the enemy concentration camp, Ann turns him over to the custody of a Dominican convent.
 After Ann learns that Carlo has died, she returns to the convent, but the Mother Superior (Laura Hope Crews) informs her she cannot have custody of Carlo without a husband.
 Desperate, Ann decides to enter the convent as a nun, and is able to ascertain which child is her own.
 Ann is forced to leave the order, however, when she is caught trying to leave with the baby.
 Ann returns to her family villa, immerses herself in the piano, and becomes an acclaimed concert pianist.
 Years later, after hiring an agency to track her son, Ann learns that Carlo was adopted by diplomat Marco Turina (John Halliday) and his wife Sylvia (Mona Barrie).
 A friend, Groce (Walter Kingsford), helps Ann get invited to a party at the Turina home, and there Ann sees Carlo, who is now called Guido Turina (David Scott) and is a young college student.
 A bond between Guido and Ann develops, and he confides to her that he feels a strange calling to become a musician, although his father plans for him to follow the long line of Turina men and become a diplomat.
 In order for Ann to continue to see Guido and coerce Marco to allow the boy to sing, she develops a friendship with Marco, but Sylvia misconstrues the relationship, and a desperate Ann is forced to confront her.
 Ann reveals Guido's parentage to Sylvia so that Sylvia will help the young man fulfill his true destiny.
 Ann agrees to leave, but receives her life's wish when Guido becomes an opera star."
Severus Snape is a fictional character in J. K. Rowling's "Harry Potter" series.
 An exceptionally skilful wizard, his coldly sarcastic and controlled exterior conceals deep emotions and anguish.
 A Professor at Hogwarts School of Witchcraft and Wizardry, Snape is hostile to the series' protagonist, Harry, the moment he sets foot in Snape's classroom; this hostility is rooted in Harry's resemblance to Harry's father James, who bullied and harassed Snape during their time at Hogwarts.
 Though philosophically attracted to the Dark Arts and Lord Voldemort's ideology of wizard supremacy, Snape's love for Muggle-born Lily Evans, Harry's mother, eventually compels him to defect from the Death Eaters.
 Snape becomes a double-agent on behalf of Albus Dumbledore and the Order of the Phoenix, and protects Harry throughout the series.
The gens Aurelia was a plebeian family at Rome.
 The first member of the "gens" who obtained the consulship was Gaius Aurelius Cotta in 252 BC, from which time the Aurelii become distinguished in history down to the end of the Republic.
 The Aurelii flourished under the Empire, with members of this "gens" becoming Emperors, namely Marcus Aurelius, his son Commodus, and the Severan dynasty, who through adoption assumed the nomen.
 Many later families of citizens were enrolled under the authority of these Emperors also assumed the nomen "Aurelius".
 By far the largest number were enrolled as the result of the "Constitutio Antoniniana", enacted by the emperor Marcus Aurelius Severus Antoninus Augustus, better known as Caracalla.
 The name became so common that it was sometimes abbreviated Aur., and by the latter centuries of the Empire it becomes difficult to distinguish members of the gens from other persons bearing the name.
Severus Snape and the Marauders is a 2016 American short film written by director Justin Zagri, based on "Harry Potter" characters by J. K. Rowling.
 It officially premiered on March 1, 2016 at the Youtube channel Broad Strokes Productions.
 The fan film caught the attention of BuzzFeed, "Entertainment Weekly", "Time",
This is a list of potions used in the "Harry Potter" series.
 Many are mentioned in potions class at Hogwarts, which is taught by Severus Snape in books one to five and Horace Slughorn in books six and seven.
John Lawrence Nettleship (1 August 1939 – 12 March 2011) was a British schoolteacher who taught chemistry at Wyedean School, Gloucestershire.
 His pupils there included Joanne Rowling, whose mother worked for some time as an assistant in his department.
 He has been stated to be a major inspiration for the character of Severus Snape in Rowling's "Harry Potter" series of fantasy books.
Alan Sidney Patrick Rickman (21 February 1946 – 14 January 2016) was an English actor and director known for playing a variety of roles on stage and on screen.
 Rickman trained at the Royal Academy of Dramatic Art in London, and was a member of the Royal Shakespeare Company, performing in modern and classical theatre productions.
 His first big television part came in 1982, but his big break was as the Vicomte de Valmont in the stage production of "Les Liaisons Dangereuses" in 1985, for which he was nominated for a Tony Award.
 Rickman gained wider notice for his film performances as Hans Gruber in "Die Hard" and Severus Snape in the "Harry Potter" film series.
Titus Cassius Severus (died in 32 AD) was an ancient Roman rhetor from the "gens Cassia".
 He lived during the reigns of Augustus, Tiberius and Caligula.
 Cassius Severus, a fearless fighter for freedom of speech, was sharply eloquent against the new governmental order, which finally saw him exiled and his works banned after his death.
The Order of the Phoenix is a secret organisation in the "Harry Potter" series of fiction books written by J. K. Rowling.
 Founded by Albus Dumbledore to fight Lord Voldemort and his followers, the Death Eaters, the Order lends its name to the fifth book of the series, "Harry Potter and the Order of the Phoenix".
Marcus Silius Messala (born ca.
 AD 160 – fl.193) was a Roman Politician, senator and suffect consul towards the end of the 2nd century.
 In 193, Messala was the Suffect Consul from May until June.
 He was in command of the location where the murder of Pertinax took place.
 Septimius Severus accused Messala of murdering Pertinax and using his influence to convene and order the Senate to place the Senator Didius Julianus as Emperor.
 Septimius Severus called the death of Didius Julianus divine providence and ordered the execution of Messala.