You can help expand this article with text translated from the corresponding article in Finnish. (September 2020) Click [show] for important translation instructions. Machine translation, like DeepL or Google Translate, is a useful starting point for translations, but translators must revise errors as necessary and confirm that the translation is accurate, rather than simply copy-pasting machine-translated text into the English Wikipedia. Do not translate text that appears unreliable or low-quality. If possible, verify the text with references provided in the foreign-language article. You must provide copyright attribution in the edit summary accompanying your translation by providing an interlanguage link to the source of your translation. A model attribution edit summary is Content in this edit is translated from the existing Finnish Wikipedia article at [[:fi:Cay Sundström]]; see its history for attribution. You may also add the template {{Translated|fi|Cay Sundström}} to the talk page. For more guidance, see Wikipedia:Translation.

Carl-Johan (Cay) Sundström (1 July 1902, in Hamina – 5 March 1959, in Stockholm) was a Finnish dentist, politician and diplomat. He was a member of the Parliament of Finland from 1936 to 1941 and again from 1944 to 1945, representing first the Social Democratic Party of Finland (SDP) and later the Finnish People's Democratic League (SKDL). He Joined the Socialist Unity Party (SYP), a member organisation of the SKDL.

Sundström was the chairman of the SKDL from 1944 to 1946.

From 1941 to 1944, Sundström was in prison for political reasons. He was Envoy of Finland to the Soviet Union from 1945 to 1953 and to the People's Republic of China from 1953 to 1959 (from 1954 as Ambassador).^[1]