Question: 20th Century Boys was a heavy metal pairing of German lead vocalists Michael Bormann of Jaded Heart and Michael Voss of Mad Max, the duo recorded 11 songs by T. Rex as a tribute to Marc Bolan and released them as an album called "Beware of the Rex!", Bolan was an English singer-songwriter, musician, guitarist, and poet, best known as the lead singer of which glam rock band?
Context: T. Rex were an English rock band, formed in 1967 by singer-songwriter and guitarist Marc Bolan.  The band was initially called Tyrannosaurus Rex, and released four psychedelic folk albums under this name.  In 1969, Bolan began to shift from the band's early acoustic sound to an electric one.  The following year, he shortened their name to T. Rex.  The 1970 release of the single "Ride a White Swan" marked the culmination of this development, and the group soon became a commercial success as part of the emerging glam rock scene. Marc Bolan ( ; born Mark Feld; 30 September 1947 – 16 September 1977) was an English singer-songwriter, musician, guitarist, and poet.  He was best known as the lead singer of the glam rock band T. Rex.  Bolan was one of the pioneers of the glam rock movement of the 1970s.  He died at age 29 in a car accident a fortnight before his 30th birthday. 20th Century Boys was a heavy metal pairing of German lead vocalists Michael Bormann of Jaded Heart and Michael Voss of Mad Max.  The duo recorded 11 songs by T. Rex as a tribute to Marc Bolan and released them as an album called "Beware of the Rex! " in 2004.  This was only a one-time project for Bormann and Voss. Mickey Finn or occasionally Micky Finn (especially on Beat Club), (born Michael Norman Finn, 3 June 1947 – 11 January 2003) was the percussionist and sideman to Marc Bolan in his band Tyrannosaurus Rex (on one album, "A Beard of Stars"), and later, the 1970s glam rock group, T.Rex.  Often confused with other musicians by the same name, Michael Norman Finn (apart from T. Rex) only toured as a sideman in the 1960s with Hapshash and the Coloured Coat.  After Bolan and T.Rex's demise, he worked as a session musician for The Blow Monkeys and The Soup Dragons. "Truck On (Tyke)" is a 1973 single by the British glam rock band T. Rex.  Neither the track nor its B-side, "Sitting Here", appeared on an original T. Rex studio album, but both were added as bonus material on re-releases of the 1974 album Zinc Alloy and the Hidden Riders of Tomorrow.  The record was poorly received critically and did not perform as well in the charts as previous T. Rex singles.  The single was in the UK charts for a total of eleven weeks, peaking at No. 12, Truck On (Tyke) was the last T. Rex single to break the top 20 until 1975's New York City.  Marc Bolan acknowledged that "Truck On (Tyke) is my 14th hit record and I wouldn't be at all surprised if it didn't make number one."  Later, Marc would claim the move to be deliberate, stating that its release "was a planned thing.  I wanted something not so good to happen to compare it (future material) against." Billy Super Duper is an album by English glam rock act T. Rex.  Released in 1982 by record label Marc on Wax, it was the first LP of entirely new and unheard material released after Marc Bolan's death in 1977 as the previous posthumous release, "You Scare Me to Death" consisted of demos first released in 1974.  Billy Super Duper consists of studio outtakes and home demos recorded by the band between 1972 and 1977, with arrangements produced by John and Shan Bramley (the heads of the Marc Bolan Fanclub at the time).  The album was intended to "complete" the demos and bring them up to date with contemporary music. Beware Of The Rex!  is the only album released by the 20th Century Boys.  Recorded in 2003, it was released just over a year later by Ulftone Music and was a tribute album to Marc Bolan of the British band T. Rex.  The grouping was just a one-time project and only planned to release this one album. "Zip Gun Boogie" is a 1974 single, originally credited in the UK as a solo single by Marc Bolan of the British glam rock band T. Rex.  In other territories, the single was credited to "T. Rex" or "Marc Bolan and T. Rex"; almost all reissues of the track credit it solely to T. Rex.  The track and its B-side feature on the 1975 T. Rex album Bolan's Zip Gun. Bolan Boogie is a compilation album by English glam rock act T. Rex.  After Marc Bolan had left Fly Records to form his own label distributed through EMI/T.  Rex Wax Co, his former label released this "best of" compilation in 1972 with recent single A- and B-sides, many of which had not appeared on previous albums.  Also included are songs from the early Tyrannosaurus Rex albums. Light of Love is a US-only album released by British rock band T. Rex in 1974.  It is composed of 3 tracks previously released in the UK on the album "Zinc Alloy and the Hidden Riders of Tomorrow", together with 8 songs recorded in the Spring of 1974 at Music Recorders Inc.  Studios in Hollywood which would later appear on the album "Bolan's Zip Gun".  The album was engineered by Gary Ulmer and, in the absence of Tony Visconti (who had left T. Rex production duties), was produced by Marc Bolan himself.  The album marked the first time that a T. Rex album had been produced without Tony Visconti and also marked Bolan's debut in this role.
Answer: T. Rex