Quentin Coldwater, Eliot Waugh and Julia Wicker are loosely based (according to Lev Grossman, the author of the book trilogy the show is based on) on the characters of Charles Ryder, Lord Sebastian Flyte and Lady Julia Flyte from the book, Brideshead Revisited by Evelyn Waugh. The characters of Sebastian and Julia Flyte are siblings.
Jason Ralph (Quentin Coldwater) has been married to actress Rachel Brosnahan since 2016. Stella Maeve (Julia Wicker) and Rachel have both appeared separately in the TV show, Gossip Girl (2007). They played Emma Boardman and Girl respectively.