Marvel Movies

Theresa Cassidy

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Theresa Cassidy
Alias(es) Siryn
Appeared in X2: X-Men United
X-Men: The Last Stand
Status Alive
Actor Shauna Kain

Siryn is a mutant who can produce powerful screams from her vocal cords.


X2: X-Men United

Theresa Cassidy was a student at Xavier's School for Gifted Youngsters. During William Stryker's attack on the mansion, her scream alerted the rest of the school that they were under attack. She was captured, but was rescued by Colossus.

X-Men: The Last Stand

Theresa was one of the students at Xavier's funeral.



  • Canon (2 films)


  • Her name also appears on a list of names Mystique scrolls through on Stryker's computer while looking for Magneto's file.
  • In the comics, Sean Cassidy is her father. However, in the films, Sean died before 1973 making it near impossible for him to be Theresa's father.


To be added

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