J.K. Rowling created Armando Dippet as the Hogwarts headmaster before Albus Dumbledore. Dippet is identified as headmaster during Tom Riddle’s time as a student at Hogwarts.
In the Harry Potter backstory, Dippet leads the school when Riddle opens the Chamber of Secrets and a student, Myrtle Warren, dies. Riddle persuades Dippet that the incident was an accident, helping him avoid expulsion. Dumbledore, then a Transfiguration teacher, is more suspicious of Riddle’s account.
Dippet is mentioned and shown in material connected with the series, including a portrait and supplementary Harry Potter information. He should not be confused with Phineas Nigellus Black, another former headmaster, or Minerva McGonagall, who succeeds Dumbledore much later. Dippet’s role is mainly historical, but it helps establish the school’s leadership during the series’ crucial earlier events.