Siryn

Theresa Maeve Rourke Cassidy, better known as Siryn, carries one of the most storied bloodlines in Marvel's mutant mythology — she is the daughter of the original Banshee, Sean Cassidy, and inherited his devastating sonic scream along with the strength of her own fierce identity. Her first appearance in Spider-Woman #37 (1981) is a genuine sleeper key, making it a high-priority pickup for serious X-Men collectors who want to get ahead of the curve on a character whose importance to the broader mutant universe only grew over the decades that followed.

Siryn found her true home in X-Force, joining the team during its early-to-mid 1990s run and quickly becoming one of its most compelling members. Her complicated relationship with Deadpool — one of the more unexpectedly tender dynamics in Marvel comics — gave her emotional depth that set her apart from her teammates. She also anchored significant storylines involving the Cassidy family legacy, her struggles with alcoholism (a trait painfully shared with her father), and her evolving sense of leadership. These arcs transformed her from a supporting player into a fully realized hero with genuine pathos.

Her time with X-Factor Investigations, written by Peter David, pushed Siryn into even more dramatic territory. The shocking storyline surrounding her pregnancy and its devastating aftermath ranks among the most emotionally affecting mutant stories of the late 2000s, cementing her as a character capable of carrying heavyweight narratives. She later took on the mantle of Banshee in a bold move that honored her father's legacy while staking out her own mythological ground, adding a divine dimension to her already formidable power set.

For collectors, Siryn's key books span multiple decades and multiple team titles, making a complete run a rewarding and genuinely challenging chase. Spider-Woman #37 leads the list as her debut, while her early X-Force appearances and the landmark X-Factor Investigations issues round out a collection that tells the story of one of Marvel's most underrated mutants. As X-Men properties continue to command attention in broader pop culture, Theresa Cassidy's books represent smart, character-driven collecting with real upside.