Background: A Night at the Opera is the fourth studio album by the British rock band Queen, released on 21 November 1975 by EMI Records in the United Kingdom and by Elektra Records in the United States. Produced by Roy Thomas Baker and Queen, it was the most expensive album ever recorded at the time of its release. The album takes its name from the Marx Brothers film of the same name, which the band watched one night at the studio complex when recording. A Night at the Opera incorporates a wide range of styles, including ballads, songs in a music hall style, hard rock tracks and progressive rock influences.
Context: "Death on Two Legs" can be referred to as Freddie Mercury's hate letter to Queen's first manager, Norman Sheffield, who for some years was reputed to have mistreated the band and abused his role as their manager from 1972 to 1975. Sheffield denied the allegations in his 2013 autobiography entitled "Life on Two Legs: Set The Record Straight", and referred to copies of the original 1972 management contracts between Sheffield and Queen, which were included in the book as proof of his defence. Though the song never makes direct reference to him, after listening to a playback of the song at Trident Studios during the time of album release, Sheffield was appalled, and sued the band and the record label for defamation, which resulted in an out-of-court settlement, but also confirmed his connection to the song.  During live performances, Mercury would usually rededicate the song to "a real motherfucker of a gentleman", although this line was censored on the version that appeared on their Live Killers album in 1979. Other than on the live album, he said it was dedicated to a "motherfucker I used to know".  In the Classic Albums documentary about the making of A Night at the Opera, Brian May stated that the band was somewhat taken aback at first by the bitterness of Mercury's lyrics, and described by Mercury as being "so vindictive that he [May] felt bad singing it". After the song came together, it was agreed that the "author should have his way", and the song was recorded as written.  As with "Bohemian Rhapsody", most of the guitar parts on this song were initially played on piano by Mercury, to demonstrate to May how they needed to be played on guitar. "Death on Two Legs" remained on the setlist until, and well into, The Game Tour in 1980, and was then dropped. However, the piano introduction was played during the Hot Space and Works tours.
Question: Why did he hate him?

Answer:
was reputed to have mistreated the band and abused his role as their manager from 1972 to 1975.