While many of Battlestar Galactica's Cylons can be recognized by eight distinctive model numbers, the Significant Eight, the Final Five Cylons stand definitively apart. They do not have numbers, only names, and exist as individuals rather than iterations of a widespread model. The Final Five's lack of model number is just one of many indicators that they are different from the other Cylons of the series.
Throughout most of Battlestar Galactica, the Final Five are constantly being hidden and manipulated by model Number One, John Cavil. Cavil's schemes leave humans and Cylons alike wondering about the Final Five. Their true identities and origins finally become clear near the end of the series when it is revealed that the original "Earth" was inhabited by a sentient race of humanoid Cylon models who were destroyed in a nuclear attack. Only five humanoid Cylons remained: the Final Five.
Why The Final Five Don't Have Model Numbers
The Final Five don't have model numbers because as the last survivors of Earth, they are the original form of Cylon, and actually created the Significant Eight models and system. Although they personally had names, the Final Five decided to give only model numbers to the eight humanoid Cylon models they created. The Significant Eight later earned their own names, though they shared their appearance. In this way, Battlestar Galactica's the Final Five are the ancient creators of the eight humanoid Cylon models.
The Final Five created Battlestar Galactica's eight Cylon models to avoid even more Cylon rebellions in the long historical chain of Cylon/Human war. Along with hoping to warn humans about the dangers of Cylon rebellion, the Final Five wanted to create a new humanoid Cylon model that is less apt to enter a war with humans. They added human qualities like love, mercy, and religion to the models so they would be less prone to violence and uprising. Unfortunately, this goal didn't succeed as Cylons like Number One actively worked against the human race, hoping for their demise.
What The Significant Eight's Model Numbers Mean
Battlestar Galactica's The Significant Eight have model numbers that signify the order in which they were created. Because John Cavil was reportedly created first, he is considered Number One. The Final Five then created Numbers Two through Eight in that order. Though some models were created before others, most of the Significant Eight maintain equal knowledge and skills. Only Number One differs because he helped the Final Five create the other models and uses this information to manipulate both the Significant Eight and the Final Five.
Throughout the Battlestar Galactica series, sequels, and reboots Cylon models have come in many different forms, representing the violent and complicated history of Cylons. As the last surviving members of the original Cylon race, the Final Five defy the model numbers they created, yet fall prey to their creations anyway, becoming pawns in the long war between Cylons and humans in Battlestar Galactica.