The veneration of saints is an important aspect of Catholic and Orthodox worship and plays a crucial role. Although modern saints such as Popes John XXIII and John Paul II have well-documented life stories, historically that's not always the case. Hagiographies, or biographies of saints, used to rely heavily on legends, myths, and traditions, making them highly unreliable before critical examination. Although some early hagiographies had some factual basis, they do not provide a complete understanding of the saint's story.
If you want to know which beloved saints probably never existed check out this gallery.