Reformist Soviet leader Mikhail Gorbachev said Baroness Thatcher was a "heavyweight politician".
He said: "Thatcher was a politician whose word carried great weight. Our first meeting in 1984 set in train relations that were sometimes complicated, not always smooth, but which were serious and responsible on both sides.
"Human relations also gradually took shape, becoming more and more friendly. In the end we managed to achieve a mutual understanding, and that contributed to a change in the atmosphere between our country and the West and the end of the Cold War.
"Margaret Thatcher was a heavyweight politician and a striking person. She will remain in our memories, and in history."
More top news
Specially-trained prison security teams have been sent to HMP Hewell near Redditch, after trouble broke out on one of the prison's wings.
Household names are among 40 women to sign open letter to BBC Director General saying he must "act now" to end pay discrimination.
"We've never actually spoken so publicly about her," the Duke of Cambridge said. "But we felt that this was the right time to do it."