Short answers, pulled from the story.
Japan claims the four southernmost islands, Iturup, Kunashir, Shikotan, and the Habomai islets, which it calls the Northern Territories, on the grounds that they were never legitimately ceded. Russia holds the islands under the terms of the 1945 Yalta Agreement, which promised the Kuril chain to the Soviet Union in exchange for entering the Pacific War, and Soviet forces occupied the islands between the 18th and the 31st of August 1945.
The name Kuril derives from kur, the Ainu word for 'man', reflecting the Indigenous Ainu people who inhabited the islands from early times. Russians later associated the name with their word kurit', meaning 'to smoke', because the volcanic plumes rising from the islands resembled columns of smoke.
The Kuril Islands chain has around 100 volcanoes, approximately 40 of which are active. The highest point is Alaid Volcano on Atlasov Island at 2,339 metres; Raikoke Island's volcano erupted in June 2019, sending emissions to 13,000 metres.
In 1941, Admiral Isoroku Yamamoto assembled the Imperial Japanese Navy strike force in Tankan Bay on Iturup Island before the attack on Pearl Harbor, choosing the location for its fog cover and sparse population. American forces later bombed Japanese bases on Shumshu and Paramushir from 1943, and the United States ran Operation Wedlock, a deception that caused Japan to increase its northern Kurils garrison from 8,000 in 1943 to 41,000 in 1944.
Approximately 19,400 people live on the Kuril Islands. About 16,700 of them live on the four disputed southern islands, and around 2,600 live on Paramushir in the north; only 8 of the 56 islands are inhabited.
The Ainu inhabited the Kurils from early times, but at the end of the 19th century Japanese administration began forced assimilation, requiring Ainu people to adopt Japanese names and prohibiting practices such as animal sacrifice and tattooing. Before Japanese colonisation in 1868, about 100 Ainu reportedly lived on the islands.