Conversation so far:
What is Death on Two Legs?
The opening track to A Night at the Opera, Death on Two Legs can be referred to as Freddie Mercury's hate letter to Queen's first manager, Norman Sheffield.
Why did Freddie Mercury hate Norman Sheffield?
Norman Sheffield was reputed to have mistreated the band and abused his role as Queen's manager from 1972 to 1975.
Did Norman Sheffield actually treat the band members of Queen badly?
Norman 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.
What else did Norman Sheffield have to say about Freddie Mercury's allegations of mistreatment?
Norman Sheffield was appalled, and sued Queen and the record label for defamation, which resulted in an out-of-court settlement, but also confirmed his connection to the song
What else can you tell me about the band Queen's song, Death on Two Legs?
Brian May stated that the band was somewhat taken aback by the bitterness of Mercury's lyrics, and described by Mercury as being so vindictive that he felt bad singing it.

Question: Who was he referring to?
Self-contained rewrite: Who was Brian May referring to when he said that the lyrics of Queen's Death on Two Legs were so vindictive that he felt bad singing it?