A name becomes a classic when it has survived a century of taste shifts without ever disappearing. James, William, Henry, Thomas, Samuel and John have all been in steady use for so long that they no longer belong to any one generation. They simply belong.
What makes a classic a classic
Classics tend to share a few qualities: a long literary or scriptural history, a pronunciation that is stable across English-speaking countries, and a set of flexible nicknames. William gives you Will, Billy or Liam. James gives you Jamie or Jim. That flexibility is part of why these names endure.
Classic does not mean old-fashioned
Oscar, Arthur, Theodore and Felix all feel quietly contemporary even though each name is centuries old. The reason is simple: they never went so mainstream that they became dated. A classic with breathing room is the best of both worlds.