And there are those who are in awe of the revitalized one, the pragmatic Portuguese whose measured words always have a purpose. He is the man who would peacock on touchlines and in press conferences even before his greatness had manifested itself, achieving success with a snarl and a swagger.
You are either rooting for one or the other. Never both. For not only are Jurgen Klopp and Jose Mourinho chalk and cheese, but leaders of clubs whose rivalry has become a tribal loathing.
'Like being in the Vietnam War'
Both managers have been at their respective clubs long enough -- Klopp celebrated his second anniversary at Anfield last weekend while Mourinho is in his second season at Old Trafford -- to know that Saturday's Premier League contest between Liverpool and Manchester United is more than a football match.
The rivalry between English football's two most successful teams is a lesson in history. Rifts run deep. Feuding fans never forget.
Former Manchester United defender Gary Neville once described the fixture as a 'blood feud that's Sicilian in intensity' and ex-Manchester United boss Ron Atkinson likened going to Anfield to being in the Vietnam War after United's coach was attacked with tear gas before a league game.
In April 1992 a young Ryan Giggs was approached by a Liverpool fan as he was leaving Anfield. The supporter asked the curly-haired winger for his autograph and the Welshman obliged, writing his name on a piece of paper, only for the fan to tear it up in front of his face.
Indeed, the last time a player moved between the two clubs was in April 1964 when Mancunian Phil Chisnall joined Liverpool.
This intense contempt hasn't always been so -- in 1915 a handful of players from both clubs were banned for conspiring to fix a match so that United were not relegated, but the bitterness between the fans intensified during the 1980s and though Liverpool versus United may now be a global affair, and the main characters in this perennial mean-spirited play ever-changing, the antipathy which surrounds this fixture remains.
For Klopp and Mourinho, however -- managers who have exchanged barbed words in the past -- the weekend's clash goes further than hatred and history.
It is a critical moment, a measure of their managerial reigns in England's north west, a region 'where everything smells like football,' according to Klopp in a recent interview with author Simon Hughes.
Bringing back the glory days
Engaging and charismatic, Klopp and Mourinho are leaders charged with the same mission: to bring back success, bring back the chutzpah, to two footballing institutions that have enjoyed better times.
On Saturday, onlookers will find out which manager is closer to achieving his objective.
United's start to this Premier League campaign suggests Mourinho's men are title contenders, which would continue the former Real Madrid and Inter Milan boss' record of winning a league title in his second season at every club he has managed.
With Liverpool seven points behind joint leaders United and Manchester City, victory for the Portuguese could plausibly end Liverpool's title hopes even before the start of Halloween's tricks and treats.
However, defeat for United at Anfield -- their first fixture of the campaign against heavyweight opposition -- and Mourinho's second season revival after an indifferent first league campaign at Old Trafford could come under scrutiny.
But it is Klopp who comes into this fixture under the most pressure. After all, Mourinho's men are unbeaten in the league and won three trophies last season. Klopp's has yet to accumulate any silverware at Anfield.
'The glory days are as far away as ever,' said former England captain Alan Shearer this week, while author Hughes -- who interviewed Klopp for his latest book 'On The Brink' -- believes the German is 'relying on the goodwill' of his achievements as Borussia Dortmund manager, with whom he won two Bundesliga titles.
Poor defending, poor results
The Liverpool team this son of a salesman is building is still a work in progress. They have won just one match in seven coming into this fixture, conceding 12 goals so far in the Premier League -- which is more than Swansea who are in the relegation zone.
Though Klopp's men have often dominated matches this campaign, so shoddy has their defending been that following their exit from the League Cup in September Klopp himself said he was 'really sick' of his team's frailties.
During the Reds' last league outing, the 50-year-old cut a frustrated figure against Newcastle as the newly-promoted hosts leveled courtesy of Liverpool's now familiar calamitous defending.
There were no wisecracks in the post-match press conference. There was little to smile about.
Is the task of guiding Liverpool to a first league title since 1990 starting to change the usually irrepressible former Dortmund manager?
'Every Liverpool manager that's been through the door in the last 20 years has begun with a relatively positive mindset,' says Hughes.
'It's a job that changes a person. They're certainly not the same person when they leave.
'But I've not seen a massive change in Klopp's demeanor and approach. I don't think he underestimated the scale of the job, but I think he's perhaps underestimated the frustration of the supporters.'
READ: How the English Premier League became a global playground
READ: The Premier League's 25 iconic moments
READ: The match that changed football
Liverpool's heart and mind punctured
George H.W.Bush was US President and Vogue by Madonna was No.1 in the British charts when Liverpool last won the title. It has been quite a wait. Indeed, it has been over five years since the club won a trophy.
Making Klopp's task all the harder are two key events in Liverpool's history in the last decade: The disastrous reign of George Gillett and Tom Hicks which put the Reds on the brink of administration in 2010 and the disappointment of the 2013-14 season, when Liverpool lost out on the league title in the final week of the season.
'The Hicks and Gillett reign made the fanbase very suspicious of owners' intentions, which puts more pressure on the current owners and Klopp,' explains Hughes.
'Equally, you have the disappointment of 2014. If Hicks and Gillett affected the mindset, that failure to win the title affected the heart.
'It seems that Liverpool have turned from a club that gets over the line, gets results, into a club that falls short. Klopp got to two cup finals in his first season but failed.
'There's been this perception that Liverpool played free-flowing attack during the glory years, but that isn't the case. They were streetwise.
'This Liverpool team isn't streetwise and that particularly affects the mindset of local supporters because they identify themselves as being streetwise. When they don't see that in their team, they lose patience. It's something he needs to pay attention to.'
Who will win Saturday's match at Anfield? Have your say on our Facebook page.
Mourinho -- the specialist in winning trophies
Klopp and Mourinho will use different methods in an attempt to achieve success on Saturday. To worship the cult of either is to devote oneself to different styles. With their teams a reflection of their personalities, Liverpool and United play as differently as day is to night.
Liverpool's manager is a lover of the high press; breathless, all-action counter-attacking, dubbed gengenpressing during his time in Germany.
His forwards are, to varying degrees, midfielders and he will order them to run and run. He is also a football romantic, believing success on the pitch is possible even if others have deeper pockets.
Mourinho, by contrast, is more conventional. He spends big on seasoned professionals and builds a team on solid defensive foundations, prioritizing clean sheets, points and trophies.
The Portuguese likes tall, powerful players --- United now have the second-tallest squad in the Premier League -- and employs a side full of specialists, acquiring prime poacher Romelu Lukaku and defensive midfielder Nemanja Matic in the summer.
While the big-money acquisition of Lukaku has made United more potent in attack, it was only last month that Mourinho said his team were 'humble enough' to play defensive football when necessary.
It is a strategy which might not be as electrifying as Klopp's tactics, but it is ruthlessly efficient.
'Mourinho has always had a winning mentality,' says Manchester-based journalist Richard Jolly.
'There are some very good managers out there who don't win many trophies. Last season he won the League Cup, which is something Mourinho specializes in because he knows it's the most winnable trophy, and the Europa League and Community Shield.
'Now they're getting into the habit of winning things.
'United was an oil tanker that needed turning around. It would need time, space and the right person at the wheel and the signs are that that's what they've got in Mourinho.'
'Everybody's friend but no-one's best friend'
But for all their differences, both Klopp and Mourinho are much the same in some respects. They are both demanding coaches who create strong bonds and inspire loyalty and admiration.
This week Liverpool's 20-year-old defender Joe Gomez talked of Klopp's 'emotional connection' with the players. No manager seems to embrace a player in the aftermath of victory quite like the tactile German.
'Klopp was probably more serious than I expected,' says Hughes. 'He's a very warm character, doesn't dodge any difficult questions and is prepared to speak about subjects people may veer away from. But if you upset him he'll let you know. If he doesn't like a question he'll encourage debate.
'I don't think Klopp wants to be liked by the players. One of the players told me that he's everybody's friend but he's nobody's best friend. That probably sums up the way he is.'
Mourinho is the charming son of an international goalkeeper who seduces the media and antagonizes opponents. He has an aura, though sometimes that has been punctured as his second spell at Chelsea, which ended in unrest, attests to.
'He knew everybody so deeply that he could control our emotions in every situation,' former Porto goalkeeper Vitor Baia once said of his former boss.
Old Trafford under his stewardship seems a happier place this season, though winning always helps morale.
Visit CNN.com/sport for more news and videos
Jolly tells CNN Sport: 'Last season you had the situation where he was criticizing players a lot -- Anthony Martial, Luke Shaw, Henrikh Mkhitaryan -- and you were wondering whether it was going to be a repeat of what happened during his second spell with Chelsea where he was falling out and losing faith of some of the players.
'But if you look at Martial and Mkhitaryan, that policy seems to have brought out the best in them. While the public see Mourinho as the controversial manager, within the game he's had a different reputation.'
Win at Anfield on Saturday and Mourinho's standing will be further enhanced, putting him and Klopp even further apart and on, for this season at least, entirely different missions.