0

0' was a malevolent entity from another dimension. Approximately two million years ago, a young Q encountered 0 after an encounter with the Guardian of Forever, and the two cosmic beings became traveling companions.

With Q's assistance, 0 used the Guardian of Forever to bring into the Universe the beings known as Gorgan, The One, and (*), and the group committed many atrocities, including the destruction of T'Kon Empire.

The Q-Continuum eventually banished 0 beyond the Galactic Barrier, where he remained for a million years.

In 2374, 0 manipulated Professor Lem Faal and the crew of the USS Enterprise-E into breaking through the galactic barrier, but was defeated once more. (TNG novels: The Q Continuum, Book 1: Q-Space, Book 2: Q-Zone, Book 3: Q-Strike)