Top 10 Side Characters With the Most Shocking Villain Arcs

10. Ben Linus (Lost)

Ben starts as a mysterious yet seemingly reasonable member of the Others on the island. As the seasons unfold, his layers of manipulation and control reveal a man willing to sacrifice anyone for his vision of the island’s destiny. What initially feels like calculated survival tactics gradually hardens into outright villainy, marked by ruthless leadership and constant deceit.

9. Agatha Harkness (WandaVision)

Agatha poses as the nosy yet friendly neighbor “Agnes” in WandaVision, quietly observing and manipulating events while hiding her true identity as a powerful witch. What begins as curiosity soon turns into a calculated scheme to steal Wanda’s magic, revealing her as the hidden villain pulling the strings behind the illusion.

8. Castiel (Supernatural)

Castiel enters as an angelic ally, helping the Winchester brothers in their fight against demons. But repeated conflicts and celestial politics push him toward increasingly ruthless decisions in the name of the greater good. His loyalty begins to fray, and in certain arcs, he emerges as a dangerous opposing force.

7. Angela Moss (Mr. Robot)

Angela begins as Elliot's loyal childhood friend and coworker fighting the same corporate enemy. Her personal losses and manipulation push her deeper into the conspiracy until her choices align with destructive forces. She shifts from supportive ally to someone whose actions make her part of the real antagonistic system.

6. Syndrome (The Incredibles)

Buddy Pine idolizes Mr Incredible as a young fan and side character dreaming of heroism. But rejection fuels his resentment and he builds a tech empire to fake heroics and eliminate real supers. His childhood admiration slowly morphs into a deadly plan that makes him the true villain of the story.

5. Trish Walker (Jessica Jones)

Trish starts as Jessica's supportive adoptive sister and a public figure seeking justice. However, trauma and a drive for power lead her to experiment with enhancements and take extreme vigilante actions. Her good intentions twist into obsession turning her into the season's main adversary against her own sister.

4. Harvey Dent (The Dark Knight)

Harvey starts as Gotham's idealistic district attorney and a strong ally to Batman and Gordon. After surviving an explosion and losing Rachel his grief turns him into Two-Face. He begins seeking fair revenge through coin flips which escalates into outright villainy and threats against everyone he once protected.

3. Theon Greyjoy (Game of Thrones)

Theon Greyjoy starts off as a cocky, conflicted outsider in Game of Thrones, constantly torn between his loyalty to the Starks and his need to prove himself as a true Ironborn. His turn toward villainy at Winterfell is driven by insecurity, pride, and a desperate hunger for validation. What follows is a downward spiral with harrowing consequences, making Theon feel more tragic than purely evil.

2. Saruman (The Lord of the Rings)

Saruman begins as a wise leader of the wizards and an ally to Gandalf. Over time, his desire for power drives him toward the dark arts and into an alliance with Sauron. He raises an army to conquer Middle-earth, betraying the free peoples and proving how even the greatest minds can fall when consumed by the need for control.

1. Peter Pettigrew (Harry Potter series)

Peter begins as one of James Potter’s loyal friends and a member of the Marauders. Over time, he betrays his closest companions by joining Voldemort and revealing the Potters’ hiding place. His cowardice and ambition transform him from a harmless sidekick into the man who enables major tragedies and ultimately serves the Dark Lord.