Keep these deceased characters in mind
Even though Severus Snape, Cedric Diggory, and Bellatrix Lestrange met early deaths throughout the Harry Potter saga, their legacies play a key role in Cursed Child.
If you do (or do not) recall: Snape, after six books of speculation, was a double agent inside the Death Eaters to ensure Harry's safety, fueled by his love for Lily Potter. He died in the Battle of Hogwarts, but not before showing Harry all of his memories and revealing his true allegiance. Because Harry's son is named after him, Snape's legacy is sure to play a role in this play.
Diggory was Harry's competitor in the Goblet of Fire. In the final round, Peter Pettigrew killed him on Voldemort's orders. He was the first person, but certainly not the last, Harry saw die during the Dark Lord's campaign.