Mr. Satterthwaite is a well-off bachelor in his sixties who is a connoisseur of the arts and a gourmet who has a cordon bleu
chef. He is something of a snob, and knows everybody who is anybody. He is described in 'The Coming of Mr. Quin" as "a bent dried-up man with a peering face oddly elflike, and an intense and inordinate interest in other people's lives." The introduction to The Mysterious Mr. Quin
(Penguin, UK, 1953) describes him as "the gossip, the looker-on at life, the little man who without ever touching depths of joy and sorrow himself, recognizes drama when he sees it, and is concious that he has a part to play.
In The Mysterious Mr. Quin
, he meets Wikipedia page on Harley Quin
.UK Agatha Christie website on Mr. Satterthwaite