Though the first half-ghost shown in the series is Danny Phantom himself, he was not the first half-ghost to come into existence. During Jack Fenton's and Vlad Masters' college days, Vlad became the world's first half-ghost when he was caught in the blast of Jack's prototype Ghost Portal. Twenty years later, Danny would go on to suffer a similar accident inside Fenton Works' completed Ghost Portal, becoming a half-ghost himself.
Half-ghosts have access to ghost powers such as intangibility, invisibility, and flight. Half-ghosts can use the majority of their powers while in human form, but in order to use them to their full potential they must change into ghost form, a transformation which Danny refers to as "Going Ghost."
- Not everyone can become a half-ghost, if Sam or Tucker gotten caught in the middle the Fenton's malfunctioning Ghost Portal, it would have likely killed them.