Question: What type of musical profession does Mike McColgan and Shagrath have in common?

Context paragraphs:
The Gang's All Here (album): The Gang's All Here is the second album released by American Celtic punk band the Dropkick Murphys.  It is their first album with Al Barr (ex-vocalist for The Bruisers) who replaced founding singer Mike McColgan in 1998 after he left the band to become a firefighter, and later form his own Punk Rock band Street Dogs.  With Barr, the band released their first 7" EP together, 1998's "Curse of a Fallen Soul" prior to recording the album.  "10 Years of Service" was the album's first and only single and music video, which got some minor airplay on MTV's 120 Minutes, a first for the band.

Ken Casey: Kenneth William "Ken" Casey Jr. (born April 15, 1969) is the bass guitarist, primary songwriter, and one of the lead singers of the Boston Celtic punk group the Dropkick Murphys.  Casey was one of the original members, starting the band in 1996 with guitarist Rick Barton and singer Mike McColgan.  He is the only original member of the Dropkick Murphys left in the band, though drummer Matt Kelly joined shortly after formation in 1997.  He is known for his melodic vocal parts and solid punk rock bass playing.  Dropkick Murphys released their ninth album "11 Short Stories of Pain & Glory" on January 6, 2017.  Casey also founded the charity group The Claddagh Fund, owns his own bar in Boston and runs his own boxing promotion called Murphys Boxing.  Casey has a small role in the 2016 film Patriots Day which is about the 2013 Boston Marathon bombing and the subsequent terrorist manhunt.

Al Barr: Alexander Martin Barr (born January 21, 1968) has been the lead singer of the Dropkick Murphys since 1998.  He was also a founder and lead singer for The Bruisers, which he helped form in 1988 in Portsmouth, New Hampshire.  His first band circa 1984, was called D.V.A. (Direct Vole Assault).  He also went on to front 5 Balls of Power, with future members of Scissorfight, The Radicts, L.E.S. Stitches, and US Bombs, before he formed The Bruisers.  His band the Bruisers had played many shows with Boston's Dropkick Murphys, and when Dropkick lead singer Mike McColgan quit the band in 1998 the Murphys asked Barr to be the new lead singer.  The first album the Dropkick Murphys released with Barr as singer was 1999's "The Gang's All Here".

Shagrath: Stian Thoresen (born 18 November 1970) is a Norwegian musician best known as the vocalist, founding member and multi instrumentalist of Dimmu Borgir.

Tzofei Tel Aviv: Tzofei Tel Aviv (or Tel Aviv Scouts in English) is a musical group originating from Israel.  The performers are teenagers, picked out of the Israel Scouts in Tel-Aviv, Israel.  They tour around the world, performing mostly Hebrew songs for Jewish organizations and others the world over.  For example, they performed Yom Ha'atzmaut concerts in Lima and Guayaquil in June 2003, as they did in St. Louis Park, MN, in 2006.  The group's musical director is Moishele Yosef, who has various other jobs in the musical profession.

Do or Die (Dropkick Murphys album): Do or Die is the first album released by Boston's Irish-American punk band, Dropkick Murphys.  It was released in 1998.  A music video for the single "Barroom Hero" was released.  This is the only album that featured original lead vocalist, Mike McColgan who went on to become a fireman before forming his own band, the Street Dogs.

Mike McColgan: Michael "Mike" McColgan is best known as the original lead singer of the American outfit Dropkick Murphys and the lead singer of the Street Dogs.

Hearts of Hoodlums: Hearts of Hoodlums is the second full-length album by the punk band Whole Wheat Bread.  It was released on January 20, 2009, though it became available to download on iTunes on January 6, 2009.  This album is said to have received help from Lil Jon, Tim Armstrong, Murs, and Mike McColgan.

Savin Hill (album): Savin Hill is the first album by punk band Street Dogs.  This is the first new material featuring lead singer Mike McColgan since he quit Dropkick Murphys in 1998.  The album is named after Savin Hill, a small area within the Dorchester neighborhood of Boston, Massachusetts.

Street Dogs: Street Dogs are an American punk rock band from Boston, Massachusetts formed in 2002 by former Dropkick Murphys singer Mike McColgan.

Supporting paragraphs: Mike McColgan Shagrath
Answer: singer