Ola Ullsten
Liberal People's Party leader who served as Prime Minister of Sweden for one year — 18 October 1978 to October 1979 — at the head of a single-party Liberal minority caretaker cabinet between Thorbjörn Fälldin's first and second tenures, after the bourgeois three-party coalition collapsed over nuclear-power policy.
Ola Ullsten served as Deputy Prime Minister in the Fälldin I cabinet from October 1976. When that three-party government collapsed on 18 October 1978 over irreconcilable Centre / Liberal / Moderate positions on nuclear power, Ullsten was elevated to the premiership at the head of an unusual single-party Liberal minority caretaker — the Liberalerna holding office without a parliamentary majority while the bourgeois bloc regrouped.
The Ullsten cabinet legislated little. Its political function was structural: keeping the right-bloc government formally in place between Thorbjörn Fälldin‘s first and second tenures so that 1976 to 1982 reads in retrospect as one continuous non-S period rather than a clean 1976-to-1978 interruption. That gap-filling role is why the Ullsten cabinet is remembered more as institutional plumbing than as a programme of its own.
After the 1979 general election returned the right bloc, Ullsten handed the premiership back to Fälldin for the Fälldin II cabinet. He continued as Liberal leader and later in international and diplomatic posts, but the 1978–1979 caretaker remains his signature tenure in Swedish political memory.