Karl Kustav Kalkun (April 9, 1927 Tartu – February 21, 1990 Tallinn) was an Estonian actor.

Karl Kalkun was born in Tartu as one of three children to. Karl Kalkun Sr., a stage manager of the Vanemuine theatre, and Emma Helene Kalkun (née Engelbär). He was the nephew of discus and hammer thrower Gustav Kalkun. In 1946, he graduated from secondary school at Tartu Secondary School No. 1 (now, the Hugo Treffner Gymnasium). In 1956 he graduated from Tartu State University's department of law.

From 1951 until 1958, he worked at Vanemuine theatre. From 1958 until 1965, he worked at the Estonian Drama Theatre. From 1965 until 1978, he was employed at the at Estonian Youth Theatre. From 1978 until 1990, he worked at the Estonia Theatre. Besides theatre roles he played also in several films.

Kalkun first married Estelle Piirand. The couple had one son, Andres. They later divorced. His second marriage was to Mare Kiisküla, with whom he had two sons, sports journalist Kristjan Kalkun and lawyer Kaarel Kalkun. The couple were still married at the time of his death.

On 21 February 1990, Kalkun was at the Eesti Televisioon (ETV) studios in Tallinn during the filming of an interview and career and life retrospective with journalist and actress Anne Tuuling when he died of a heart attack, aged sixty-two.