It sounded as if a friend were calling.

“Sorry, Emmanuel,” said President Volodymyr Zelensky of Ukraine, answering his phone in the middle of an online news conference in late March. “I have just a conversation with journalists. Can I be back in some minutes?”On the other end of the phone was Emmanuel Macron, the French president, calling directly. He could wait, it seemed.

“Yeah, please. Thank you, thank you, Emmanuel! OK, great, great. Bye-bye,” Mr. Zelensky continued, before hanging up and telling the journalists that he talks to Mr. Macron nearly every day.

That call, according to interviews with 11 people who have worked closely with either Mr. Macron or Mr. Zelensky, reflected a genuine bond between the two leaders, marked by mutual respect, trust and personal regard. That connection, many of those people say, is built on the bedrock of one common interest — defending Ukraine’s sovereignty and deflecting further Russian encroachment.

Mr. Zelensky and Mr. Macron in 2022 after a news conference in Kyiv, Ukraine.Credit…Alexey Furman/Getty Images

The people interviewed were present at critical points since the two men met. And they offer a portrait of a relationship that goes beyond a strategic partnership over the war between Russia and Ukraine.

“They have a rare relationship of trust and accountability,” said Alice Rufo, the director general for international relations and strategy at the French defense ministry and who was Mr. Macron’s deputy diplomatic adviser until 2022.