Sidney Avner was a Young Communist League (YCL) and Communist Party member from Upper Clapton, Hackney, London. He attended Davenant Foundation School and lived at at 55 Clapton Common. He was a striking figure standing well over 6ft tall.
As a member of a ten strong British Unit in the German Thaelmann Battalion fighting for the Republican cause in Spain. He and his comrades were dug in outside Boadilla in December 1936. When the British attacked the fascists on 20th December, it left eight of the ten British International brigadiers, all Communist Party members dead.
Those killed were Harry Addley (Folkestone), William Gough (Luton), Martin Messer (London), Lorimer Birch (London), Ray Cox (Southampton) and Sid Avener. The only two to survive were Esmond Romilly and Bert Ovenden.