Lord Sinderby is the father of Atticus Aldridge, who just married Lady Rose Crawley on the TV series Downton Abbey. Lord Sinderby does not approve of the interfaith marriage -- the Sinderbys are Jewish, the Crawleys are Anglican -- but after the wedding he does try to forge relationships with Crawleys. He invites the Crawleys to a shooting party in Northumberland. (He’s rented the castle.) During afternoon tea, Diana Clark shows up with Lord Sinderby’s illegitimate son. Lady Rose intervenes on behalf of her father-in-law and saves him from embarrassment. Lord Sinderby thanks Lady Rose and asks her (and Lady Mary and Robert) to keep his secret. There's nothing like juicy gossip to bring two families together.
Lord Sinderby is portrayed by actor James Faulkner. While he's been in many films and TV shows in the UK, American viewers will likely recognize him as Uncle Geoffrey from the Bridget Jones' Diary films.
[Check out the "Most Interesting Finds" on Amazon ]