MOSCOW — The figure skater Evgenia Medvedeva of Russia was already a two-time world champion and a consensus favorite to win gold at the 2018 Winter Olympics weeks before her 18th birthday last autumn.

At a competition in Moscow in October, she laughed easily. Months earlier, she had skated as the anime character Sailor Moon, dressed as a Japanese schoolgirl turned superhero. Now she performed as Tolstoy’s tragic Anna Karenina, joking, “I’m skating to show that I won’t be an old maid.”

She carried a toy cat like a security blanket but also became the assertive face of Russia’s Olympic athletes. She argued forcefully — and successfully — at a December meeting of the International Olympic Committee that all Russian athletes should not be barred from the 2018 Games because of a state-sponsored system of doping at the 2014 Games in Sochi, Russia.

Medvedeva and her training partner, Alina Zagitova, 15, are widely expected to win two of the three available medals in women’s singles skating at the Winter Games and are expected to make Russia a gold medal favorite in the team competition. But no longer does Medvedeva appear invincible. And neither does Russian skating.