* [[ActingForTwo Acting for Three]]: Paul Wesley is portraying Stefan, one of the three central protagonists. [[spoiler:In Season 4, it's revealed Stefan's ancestor is Silas and he is Silas' doppelganger. It's revealed in Season Five, there is one other doppelganger of Silas' alive in the present day, Tom Avery, an innocent paramedic.]]
** [[ActingForTwo Acting for Four]]: ... in Nina Dobrev's case. She portrays Elena the protagonist, also Katherine a villain and one of the major antagonists. In Season Five Nina Dobrev also portrays Amara, the original Petrova, and Elena and Katherine are her doppelgangers. On the spin-off [[Series/TheOriginals]], she portrays Tatia in flashbacks to the 10th century and Katherine' is ''her'' doppelganger.
* HeyItsThatGuy:
** Anna is [[{{Unfabulous}} Geena Fabiano]].
*** Her mother is played by Creator/KellyHu.
** [[Series/{{Heroes}} Adam Monroe]] is Elena and Jeremy's uncle, [[spoiler: as well as Elena's birth father.]]
*** Another one for ''Series/{{Heroes}}'' fans: Noah Bennet is Caroline's dad.
*** Gretchen is the [[spoiler: first vampire to be sired to Damon]].
** [[Series/TheLWord Jenny Schecter]] is Alaric's wife and [[spoiler: Elena's birth mother.]]
** Bonnie's Grandma is [[Series/DeadLikeMe Roxy]].
** Rebekah is [[Series/H2OJustAddWater a mermaid]].
*** She's also [[Series/PrettyLittleLiars Samara]].
*** And an [[HilariousInHindsight ironic twist]], Maya is Bonnie's ancestor, Emily.
*** Plus, Melissa's no longer dating a doctor, now that she is one.
** Hayley is also [[Series/JustAddWater a mermaid]].
** Sarah, [[spoiler: the girl Tyler kills]] is [[CoryInTheHouse Meena]].
*** Also, she's [[Series/DesperateHousewives Ana Solis]].
*** Her best friend that Katherine kills is [[Series/SuiteLifeOnDeck London Tipton's former roommate]].
** Caroline's mom is [[Series/KyleXY Nicole Trager]].
** Sage is [[Series/{{Smallville}} Tess Mercer]].
** Stefan was [[AmericanDreams JJ's friend]] and [[Film/{{Fallen}} an angel]].
*** He was also Sage's [[spoiler:[[Series/{{Smallville}} half-brother Lucas]]]], even though they never appeared on-screen together.
** [[Series/{{Degrassi}} Mia]] is now torn between vampires.
** So Tyler used to be friends with [[TheSecretCircle Faye Chamberlain]]?
** [[Series/OneTreeHill Lucas's girlfriend Lindsay]] is a werewolf.
** Creator/GinaTorres is Bree.
** Bonnie's human father was a [[Series/{{Supernatural}} vampire on another show]].
** [[SeventhHeaven Simon Camden]] is Ray.
** [[Series/TheOC Julie Cooper]] is Matt and Vicki's mom.
** April used to be friends with [[TheNineLivesOfChloeKing Chloe King]].
** [[Series/{{Arrow}} Green Arrow]] is Brady.
** [[Film/LegallyBlonde Warner Huntington III]] is Alaric.
** [[WizardsOfWaverlyPlace Stevie Nichols]] is Megan
*** She's also [[LemonadeMouth Stella]] and Ray is Luke.
** In a humorous example Nina Dobrev and Dillon Casey (who played Noah), both once played the romantic leads in a LifetimeMovieOfTheWeek
** [[TheLeague Shiva Kamini Soma Kandarkram!]]... is Qetsiyah.
** Aaron used to be [[LifeUnexpected Lux's teacher]]
** Damon and Series/{{Dexter}} have the same dad...that makes perfect sense.
** Kai used to sleep with [[TheCarrieDiaries Carrie Bradshaw]] when she was in high school.
* HeyItsThatVoice: Jason Spisak ([[VideoGame/FalloutNewVegas Vulpes Inculta]], [[WesternAnimation/YoungJustice Kid Flash]], [[WesternAnimation/GreenLanternTheAnimatedSeries Razer]]) provides the voice of Silas.
* IKnewIt: Show of hands: how many of you called [[spoiler: Stefan having killed his father?]] [[TheUntwist Yeah, thought so...]]
** Also in "The Departed" who guessed [[spoiler: the only way to kill Alaric would be to kill Elena and turn her into a vampire.]]
** Is there anyone who actually thought [[spoiler: Jeremy was going to come out of the hunter storyline alive?]]
** Many people guessed the third sacrifice would have consist of twelves witches.
** Also many people predicted Silas's lover would like [[spoiler: Elena]]
* WhatCouldHaveBeen: Originally, the 4th-season-spanning [[spoiler: cure]] storyline was supposed to resolve with [[spoiler: Damon being the one to receive the cure]]. However, almost immediately after introducing [[spoiler: the cure]] as an idea, the writers were dismayed to find that a large number of fans were predicting that very outcome. So they changed mid-course, and [[spoiler: the cure was instead given to Katherine.]]
* Devon Allowitz, who played Henrik Mikaelson, is the son of crew member Michael Allowitz