What is "primogen"

Primogen is derived from "primogenitor", a word meaning the first or earliest ancestor. It may also be related to the word " primogeniture". The word primogen is used in fiction in various ways:

• Primagen (spelled slightly different, with an "a" rather than an "o"), a fictional alien monster who traveled to the beginning of time and the universe in Turok 2: Seeds of Evil
• Primogen, the chief, and usually most powerful and eldest, representative of a vampire clan within a domain in Vampire: The Masquerade and Vampire: The Requiem