Sean Cassidy is discovered by the villainous
Changeling, who invites him to join
Factor Three. Cassidy declines upon learning Factor Three's goals. Factor Three, along with
Ogre, captures him and places a headband containing explosives around his head to force him to obey their commands. Codenamed after the
banshee, a spirit from
Irish mythology, Cassidy is forced to perform various criminal missions for Factor Three. On a mission in
New York City, Banshee encounters the X-Men.
Professor X uses his
telepathy to disarm the headband and remove it, allowing Banshee to help the X-Men defeat Factor Three. Banshee joins the second group of X-Men. After a mission at
Krakoa, Banshee remains with the "New X-Men". Banshee accompanies the team on many different missions and is present for several key moments in the X-Men's history, including the first death of an X-Man,
Thunderbird. He is also a key player during the first appearance of the
Phoenix and the team's first encounter with the
Shi'ar. While with the X-Men, he falls in love with Xavier's ex-girlfriend, Dr.
Moira MacTaggert. Given his age, he frequently acts as a confidant for both Xavier and
Cyclops, eventually convincing Cyclops to change his leadership style to better suit the older, more experienced second team of X-Men. When Banshee loses the use of his powers due to damaged vocal cords, he leaves the X-Men to stay with MacTaggert. Theresa Cassidy, Banshee's daughter, is secretly raised by Banshee's cousin
Black Tom Cassidy. Theresa later develops sonic powers of her own and adopts the name
Siryn. Siryn assists Tom with his crimes until the two are defeated by
Spider-Woman and the X-Men. While in custody, Tom makes arrangements for Siryn to be reunited with her father. Banshee's powers gradually return as he heals and he remains an ally of the X-Men. He later becomes the head of the new team of young mutants
Generation X along with
Emma Frost. Banshee also serves as the leader of
X-Corps, a team of reformed mutant criminals. Banshee is killed trying to prevent a plane crash caused by
Vulcan. In his will, he gives Siryn his family castle—Cassidy Keep—as well as his pipe. When Siryn and
Jamie Madrox have a child, they name him Sean in honor of her late father. Banshee is resurrected under the control of villains twice, before being restored to life by a
Celestial Death Seed and recruited by the
Apocalypse Twins to become their
Horsemen of Death. When Banshee is taken into the X-Men's custody,
Beast concludes that healing him of the Death Seed's energy will take years and highly advanced technology. Banshee later resurfaces as part of the
Mutant Liberation Front along with
Hope Summers. After a confrontation with the X-Men and the newest incarnation of the Brotherhood of Mutants, he rejoins the X-Men. When attacking the
Office of National Emergency, Banshee is caught in an explosion and presumed dead.
House of X Banshee later appears alive and completely cured of the Death Seed's energy during
House of X. He becomes a citizen of Krakoa after it is established as a mutant nation. Banshee is considered to join Krakoa's X-Men, but loses to
Polaris. Moira MacTaggert is retroactively revealed to be a mutant with the ability to continuously reincarnate after death. After returning to life, she reveals her survival to Banshee before killing him and ripping his face off to enter Krakoa undercover. Banshee is resurrected by
the Five, but is deeply troubled by his misfortunes. This is worsened when he is temporarily possessed by the mutant Skinjacker and later coerced into making a deal with Mother Righteous, who gives him powers similar to
Ghost Rider. It is later revealed that Banshee was bound to the Spirit of Variance, a rejected Spirit of Vengeance. ==Powers and abilities==