Problem position
The goalkeeping position has been an issue at Liverpool since the decline of Pepe Reina.
Reina's reliability deteriorated in his final two seasons at Anfield, where he made eight errors leading to goals. In contrast, he had made just one such error in the previous three seasons (across 114 appearances).
The switch in style after Rafa Benitez' departure may have affected Reina's performances, and the three-time Golden Glove winner failed to produce his best under Benitez' successors.
The Spanish international had been one of the best 'keepers in England during his prime, but his increasing unreliability forced Brendan Rodgers to bring in a replacement.
Brendan Rodgers brought in Simon Mignolet from Sunderland to replace Reina in 2013, but the Belgian has failed to convince consistently between the posts for the Reds.
Jurgen Klopp snapped up Lloris Karius from Mainz in 2016, and the young German ‘keeper arrived to Anfield with a big reputation.
After wavering between the two goalkeepers at the start of last season, Klopp announced that Karius would be the club's number one. A steady spell in the team followed, but the worst was yet to come.
There were huge warning signs against both Manchester City and Roma in the Champions League quarter-finals and semi-finals respectively.
Karius was lucky to see Aleksander Kolarov's long-range strike cannon off the bar after letting it through his hands against Roma, and was similarly fortunate when Leroy Sané had a goal (incorrectly) ruled out for offside in the second leg of the semi-final after Karius made a mess of his punched clearance.
His luck ran out on the grandest stage of them all.
The German 'keeper made two staggering mistakes against Real Madrid in the Champions League final in Kiev, which Liverpool lost 3-1. He gifted Madrid the first goal of the game when he threw the ball directly against Karim Benzema's leg in the 51st minute.
Liverpool drew level through Sadio Mané, but a wonder goal from Gareth Bale restored Los Blancos' lead. In the 83rd minute, with Liverpool pushing desperately for another equalizer, Karius let Bale's speculative effort from distance squirm through his hands into the net.
There were claims from American doctors afterwards that Karius had been suffering from concussion during the game - which may have been the case - but these errors weren't an isolated incident.
Further inexcusable errors have followed in pre-season, and now Klopp has moved to shore up Liverpool's biggest weakness.
The Reds have conceded more Premier League goals (113) than any of their top six rivals since Klopp's appointment in October 2015, and the lack of a top-class 'keeper has been a thorn in Liverpool's side for some time.
Manchester United, Spurs, Chelsea, and more recently Manchester City have all benefited from the presence of world class 'keepers as their last line of defence, and Liverpool's capture of a top-tier goalkeeper has been long overdue.
Who is Alisson?
It is remarkable to think that Alisson has only spent one season in Europe as a number one.
The 6"3 Brazilian made his breakthrough at Internacional in 2013, where he ousted former AC Milan shot stopper Dida from the first team.
He captained the South American club at the age of 21, and quickly established a stellar reputation in Brazil.
He made his international debut in 2015, and signed for Roma a year later for a modest €7.5 million.
However, he served as Wojciech Szczęsny's understudy in his first season in Rome, and made just 15 appearances in cup competitions for the Serie A club.
Alisson remained Brazil's first choice 'keeper, such was the faith in his ability, despite Ederson's impressive performances between the posts for Benfica. Last summer, Szczęsny made the move to Turin to join Juventus, and Alisson assumed the former Arsenal goalkeeper's position.
The 25 year old was superb for Roma in both the Serie A and the Champions League, and his stats certainly make for impressive reading. Alisson kept 17 clean sheets in Serie A, and had the best save percentage in the Italian top flight.
"He is the number one of the number ones, the Messi of goalkeepers, because he has the same mentality as Messi," former Roma goalkeeping Roberto Negrisolo said.
"He is a goalkeeper who can define an era."
Alisson is also Brazil's undisputed number one, and played every game at this summer's World Cup in Russia.
He has amassed 31 caps to date - compared to Ederson's solitary cap - and will likely hold the jersey for years to come.
What will Alisson bring to Liverpool?
Like his compatriot Ederson, Alisson is excellent with his feet.
His distribution is generally excellent, and he is comfortable under pressure from strikers. According to Sky Sports, he made three times as many dribbles as any other 'keeper in the Italian league last season.
He also completed more passes than any other 'keeper, and like Ederson, he is adept at picking out long passes.
His anticipation is regarded as one of his most impressive attributes, and came off his line to win the ball 41 times last season, 20 more than his nearest rival.
The addition of Ederson to Manchester City's team last season was a factor in their march to the Premier League title, and the former Benfica 'keeper was a huge upgrade on Claudio Bravo.
In fact, before Alisson's transfer to Anfield, Ederson was the most expensive 'keeper of all time.
Liverpool will be hoping for a similar impact from the man keeping Ederson out of the Brazil team.
Alisson's shot stopping statistics are also hugely impressive, as can be seen by the graphic below (credit: @colintrainer).