He is the frontman, leader, primary songwriter, and sole continuous member of the masked rock band Ghost, performing live as their vocalist under the stage names Papa Emeritus and Cardinal Copia.

Jury member and journalist Jan Gradvall stated that Forge is among the "most visionary and creative in Swedish music history.

"[2] Due to "Ghost's epic progression from underground doom favorites to an arena phenomenon" in the 2010s, Loudwire named Forge the Metal Artist of the Decade.

Peter Hällje, a former bandmate of Martin Persner, claimed he designed the Papa Emeritus character in 2005, prior to the formation of Ghost.

[17] Forge is credited as Papa Nihil on the two-track release Seven Inches of Satanic Panic, which is purported by the band to have been recorded in 1969.

During the final show of A Pale Tour Named Death, Cardinal Copia was anointed and introduced as Papa Emeritus IV.

"[13] Forge claimed that "no legal partnership" ever existed between the other members and himself; they were paid a fixed salary to perform and execute the band's image as he instructed as "musicians for hire.

[30] Cardinal Copia also makes a featured appearance on the song "I'm Not Afraid" from Emigrate's November 2018 album A Million Degrees.

[31] On 22 January 2021, Papa Emeritus IV joined the Hellacopters on the Swedish television game show På spåret to perform a cover of "Sympathy for the Devil".

[32] Papa Emeritus IV also appeared at Guaranteed Rate Field on 22 September 2022 to throw out the ceremonial first pitch of the Chicago White Sox and Cleveland Guardians baseball game.

[37] The film includes a narrative story based on a web series produced by the band, which incorporates fictional characters and lore surrounding them.

[39][40] His brother Sebastian, who was thirteen years his senior, had a large influence on him and introduced him to film and music such as Siouxsie and the Banshees, Kim Wilde, Rainbow, Kiss, and Mötley Crüe at a very young age.