A large section of the fanbase have never forgiven the Spaniard, who won the Champions League and FA Cup in a six-year spell at Anfield, for describing the Toffees as a "small club" following a Merseyside derby in 2007.
Benitez has sought to clarify those comments since his departure in 2010 and, while Everton's board have looked beyond them, fans have not.
Here, the PA news agency looks at other managers to have controversially crossed the divide to manage rival clubs.
Brian Clough (Derby 1967-1973, Nottingham Forest 1975-1993)
Ever a controversial figure, Brian Clough left Derby a year after winning Division One as his gamble in a power struggle with the board backfired when he and assistant Peter Taylor resigned, expecting chairman Sam Longson to back down and hand them more control. Instead Longson accepted the resignations. After brief spells at Brighton and Leeds, Clough was appointed by Derby's arch-rivals Forest, where he would win back-to-back European Cups and another title.
George Graham (Arsenal 1986-1995, Tottenham 1998-2001)
Graham wrote himself into Arsenal's history books by guiding the club to their first league championship in 18 years with the dramatic last-day title decider at Anfield in 1989, with another title arriving in 1991. He also won the FA Cup, two League Cups and the European Cup-Winners' Cup before being sacked and banned for a year after accepting an illegal payment from an agent. A brief spell at Leeds after his return was followed by his appointment at the Gunners' north London rivals Tottenham, with whom he won the club's first trophy in eight years with the 1999 League Cup.
Harry Redknapp (Portsmouth 2002-2004, Southampton 2004-2005, Portsmouth 2005-2008)
A glutton for punishment, Redknapp swapped one South Coast club for another and then back again – all within the space of two years. He resigned as Pompey boss announcing he needed a break from football only to be appointed manager of Southampton weeks later and immediately be labelled 'Judas' by Portsmouth fans. After failing to keep Southampton in the Premier League, Redknapp left the club in the Championship when Portsmouth came calling again barely a year after moving to St Mary's.
Radomir Antic (Real Madrid 1991-1992, Atletico Madrid 1995-2000, Barcelona 2003)
Antic had the unenviable task of replacing Alfredo Di Stefano at Real and lasted just 10 months. His greatest success in Spain came at Atletico, where he won LaLiga and the Copa Del Rey. He replaced the sacked Louis Van Gaal on a six-month contract at Barcelona with the club, unbelievably, 15th in LaLiga. He gave regular appearances to youngsters Victor Valdes and Andres Iniesta but was replaced by Frank Rijkaard at the end of the season.
Sven Goran-Eriksson (Roma 1984-1987, Lazio 1997-2001)
The Swede won the Coppa Italia at the Stadio Olimpico before, after spells with Fiorentina, Benfica and Sampdoria, he returned as coach of city rivals Lazio and won the Coppa Italia twice, the Supercoppa Italiana twice, the European Cup-Winners' Cup, UEFA Super Cup and only the club's second Serie A title before moving on to become England manager.
Steve Bruce (Birmingham 2001-2007, Aston Villa 2016-2018, Sunderland 2009-2011, Newcastle 2019 – present)
Bruce has switched sides twice, albeit with a considerable period between managing one club and their rival. He oversaw Premier League promotion and relegation with Birmingham before reappearing in the Midlands almost a decade later but the best he could manage was taking Villa to the Championship play-off-final and his tenure ended with one supporter throwing a cabbage at him. Bruce, the current Newcastle manager, also previously took charge of north-east rivals Sunderland but attributed his sacking partly to the fact he was a Newcastle fan.
Sam Allardyce (Newcastle 2007-2008, Sunderland 2015-2016)
Allardyce's spell at St James' Park lasted less than a season and he was not particularly popular during that time. However, when he reappeared at struggling Sunderland seven years later he had more of an impact as he tripled their meagre points total a fortnight into the job and oversaw a 3-0 win over Newcastle. He successfully steered the club away from relegation before England came calling.
Alex McLeish (Birmingham 2007-2011, Aston Villa 2011-2012)
McLeish's Midlands swap came just five days apart and was controversial on both sides as there was a contractual dispute with Birmingham – having won the League Cup and been relegated in the same season – while fans at his new employers daubed anti-McLeish graffiti on the walls at Villa's training ground. Poor results – setting a club record four home wins all season – meant the Scot lasted only a year.
Leonardo (AC Milan 2009-2010, Inter Milan 2010-2011)
The former AC Milan player replaced Carlo Ancelotti as manager but lasted a season before quitting citing a difficult relationship with then Milan owner Silvio Berlusconi. Barely six months later Leonardo replaced Benitez at Inter and won the Coppa Italia and finished second, six points behind Milan, before resigning at the end of his first half-season.
Jorge Jesus (Benfica 2009-2015, Sporting 2015-2018, Benfica 2020-present)
Jesus won three league titles and seven other trophies before, to a huge outcry, he signed for Benfica's biggest rivals Sporting after his employers bungled contract extension negotiations. However, his biggest success was one League Cup and he returned to Benfica in 2020.