The series has a lot of characters, but these are the main few throughout the series and their first appearances.
Stephanie Edgely / Valkyrie Cain: Skulduggery Pleasant
Skulduggery Pleasant: Skulduggery Pleasant
Tanith Low: Skulduggery Pleasant
Ghastly Bespoke: Skulduggery Pleasant
China Sorrows: Skulduggery Pleasant
Mr Bliss: Skulduggery Pleasant
Fletcher Renn: The Faceless Ones
Solomon Wreath: The Faceless Ones
Caelan: Dark Days
Stephanie Edgely / Valkyrie Cain: Skulduggery Pleasant
Skulduggery Pleasant: Skulduggery Pleasant
Tanith Low: Skulduggery Pleasant
Ghastly Bespoke: Skulduggery Pleasant
China Sorrows: Skulduggery Pleasant
Mr Bliss: Skulduggery Pleasant
Fletcher Renn: The Faceless Ones
Solomon Wreath: The Faceless Ones
Caelan: Dark Days