First Appearance: Uncanny X-Men #26 (November 1966).
Appearances: Numerous others.
Years Active: ?-?
Sean Cassidy was for a time the mutant hero Banshee, a member of the X-Men. He is also the father of the mutant heroine Siryn, formerly of X-Force.
However, as Xavier Fournier points out, before the birth of his daughter Cassidy was a member of the international police force Interpol, using his powers to fight crime. Given that Siryn is a teenager, this firmly puts Cassidy in the Pre-FF #1 Hero category.