Alec Guinness recounted in his journal "A Positively Final Appearance" a story about Thesiger, saying he was once stopped by a woman while walking through Picadilly, who asked him, "Didn't you used to be Ernest Thesiger?" To which he replied bluntly, "Still am!" and hurried on.
He is interred at Brompton Cemetery in London alongside his father, mother and sister.
He used to lay lilies at the feet of the handsome doorman at the Savoy Hotel in London.
He was a great friend (and crochet partner) of Queen Mary and is even said to have based his later appearance on her.
He was an accomplished watercolor artist and embroiderer (and even published a book entitled 'Adventures in Embroidery').
He was awarded a CBE (Commander of the Order of the British Empire) in 1960 for his services to drama.
He was mentioned in dispatches for his service in World War I.
He was portrayed by actor Arthur Dignam in the 1998 film Gods and Monsters (1998), which is based on the life of his friend James Whale.
His famous role of mad scientist Dr. Pretorius in Bride of Frankenstein (1935) was initially turned down by Bela Lugosi. Universal wanted Claude Rains then to do the part but director James Whale insisted on Thesiger.
More than three decades after his death, he appeared in archive footage taken from Bride of Frankenstein (1935) in the opening credits of "Weird Science" (1994). The same is true of Boris Karloff.
Thesiger originally played the role of Theotocopolous, the anti-technology rabble-rouser, in Things to Come (1936), but he was replaced by Sir Cedric Hardwicke because the latter was considered more marketable.