Ukrainian comedian Volodymyr Zelensky has scored a landslide victory in the country's presidential election.
With nearly all ballots counted in the run-off vote, Mr Zelensky had taken more than 73% with incumbent Petro Poroshenko trailing far behind on 24%.
"I will never let you down," Mr Zelensky told celebrating supporters.
Russia says it wants him to show "sound judgement", "honesty" and "pragmatism" so that relations can improve. Russia backs separatists in eastern Ukraine.
The comments came from Russian Prime Minister Dmitry Medvedev, in a Facebook post on Monday (in Russian).
He said he expected Mr Zelensky to "repeat familiar ideological formulas" that he used in the election campaign, adding: "I have no illusions on that score.
"At the same time, there is a chance to improve relations with our country."
Mr Poroshenko, who admitted defeat after the first exit polls were published, has said he will not be leaving politics.
He told voters that Mr Zelensky, 41, was too inexperienced to stand up to Russia effectively.
Mr Zelensky, a political novice, is best known for starring in a satirical television series Servant of the People, in which his character accidentally becomes Ukrainian president.
He told reporters he would "reboot" peace talks with the separatists fighting Ukrainian forces and volunteers in the east.
"I think that we will have personnel changes. In any case we will continue in the direction of the Minsk [peace] talks and head towards concluding a ceasefire," he said.
There are sporadic skirmishes and the situation also remains tense around Crimea, annexed from Ukraine by Russia in 2014.
Time for the joking to stop
Analysis by Jonah Fisher, BBC News, Kiev
Ukrainians are waking up this morning and discovering that the last few months were not a dream.
They really have elected a man who currently stars in a TV series as the president - as the country's next real president. And it wasn't even close.
The pressure will now be on Mr Zelensky to demonstrate that he knows what he is doing.
Throughout the election campaign, he avoided serious interviews and discussions about policy - preferring instead to post light-hearted videos to social media.
He's got about a month before the inauguration. Then the comedian-turned-president will be faced with a complex in-tray that includes a simmering war with Russian-backed rebels in the east.
Mr Poroshenko, who has been in power since 2014, said the result of the election "leaves us with uncertainty [and] unpredictability".
"I will leave office but I want to firmly stress - I will not quit politics," he said.
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