See Also: Notable Characters Season 1 | Notable Characters Season 2 | Notable Characters Season 3 | Notable Characters Season 4 | Notable Characters Season 5 | Notable Characters Season 6 | Notable Characters Season 7 | Notable Characters Season 8
- "Henry Jenkins" - Found at a mobile home near the campsite where Castle allegedly spent the summer. Later we find that he's not the Real Henry Jenkins, whose DMV record was hacked to show Fake Jenkins' photo.
- Fake Jenkins - Captured in a candid photo with Castle; later appears at a warehouse in Montreal to convince Castle not to follow any leads regarding his disappearance.
- Henry Wright - Programmer by day, King of the East Mountain Goblins by night
- Dr. Elena Sarkov - Head of a secret science project attempting to create stealth technology
- Ms. Leslie Ruiz - Teacher of second grade at Kennedy Elementary School; she teaches Castle a thing or three about the nature of child wrangling.
- Emily - A student who befriends Castle; they have a princess tea party and Castle encourages her to use her princess powers for good.
- Jason - A student who doesn't think much of Castle. Beckett: "You've only been here a day and a half and you already have a nemesis?"
- Bill Garrett - Former cop in the cyber crime division, whose insight into the suspect helps find the victims in time to save them.
- Marcus Lark - Development mogul who wants to manipulate destiny in more than one dimension; fortunately he's defeated in at least two of them.
- Tobias - Shares a bunkhouse (and a bathroom) with our newlyweds, along with some case-relevant gossip; likes coffee "like I like my men: strong, black, and bitter."
- Marisa Aragon - Transit cop who trades friendly insults with Esposito while they're both held hostage; she also helps subdue the dude with the switch when the time comes.
- The action team known as The Indestructibles:
- Brock Harmon - Action star who started out as a porn star called "Brock the..."
- Clay Biggs - Another action star who "graduated top of his class at Julliard."
- Rolf Magnus - "Nordic bodybuilder and a card-carrying member of Mensa."
- Serafina - Mixed martial arts expert, part of the crew
- Trey Harmon - Brock Harmon's son, who turns out to be in debt to a drug dealer
- Enrique Gomez - The victim's childhood friend who reveals the truth about the victim's past
- Henry Allen Booth - Collects scale model cars and enjoys rumors that he's a drug dealer
Resurrection (part 1 of 2)
Reckoning (part 2 of 2)