How Volodymyr Zelensky rallied Ukrainians, and the world, against Putin.

Before Russia invaded Ukraine, President Volodymyr Zelensky was often derided as a comic turned unlikely politician. But with the help of social media, he has become the leader Ukraine did not know it needed.

Dressed in an army-green T-shirt or fleece, unshaven and wan, Mr. Zelensky has inspired Ukrainians to fight for their country — and Europeans to see Ukraine in a different light, as a victim of aggression fighting bravely for independence, freedom and democracy.