These players arrived mid-season with little time to settle in, but proved to be transformational acquisitions for their clubs.

January is often described as the bleakest month of the year, but it can also be a time of renewal, a moment to make a fresh start. And for football clubs, the opening of the January transfer window is an opportunity to breathe new life into disappointing campaigns and invest for the future.

Flagging Premier League champions Manchester City are expected to be active as they try to salvage their disastrous season, while Manchester United should use the window to begin their cultural reset by selling Marcus Rashford. Arsenal, meanwhile, can use the window to strengthen their injury-ravaged squad and boost their chances of catching leaders Liverpool.

Managers often complain that the winter window offers little value compared to the summer, when the bulk of the business is done. And yet, some of the shrewdest transfer moves have been made in the first month of the year. Here are the best January signings in Premier League history...

10 Seamus Coleman (Sligo Rovers to Everton, £60,000)

When it comes to bang for your buck, you could say Coleman is the best signing in Premier League history.Back in January 2009, David Moyes got wind of the full-back and snapped him up from League of Ireland side Sligo Rovers for £60,000 ($76,000).And no, we're not missing a zero or two.

Coleman couldn't have an instant impact as he had to have surgery on an infected blister on his toe almost immediately after joining Everton, and he later joined Blackpool on loan for half a season.But he's been a Toffee since August 2010, playing under 11 managers.

He's made 426 appearances for Everton, scoring 56 goals, which works out at £140 per appearance and a bit more than £1,000 per goal or assist. He's also been one of their most consistent performers, as well as their most loyal and passionate, resisting the temptation of big moves to stay with the club, which he's captained since 2019. He's still going strong at 36.

9 Pierre-Emerick Aubameyang (Borussia Dortmund to Arsenal, £56m)

Everyone thought Aubameyang would end up at Real Madrid when he left Borussia Dortmund, but Arsenal were the ones who got him when he left the German side in January 2018. He was the Gunners' record signing at the time, but he quickly made the fee look good with 10 goals in 13 Premier League games.

He kept it up in the next two seasons, scoring 60 times in all competitions, and almost single-handedly fired Arsenal to win the FA Cup in 2020, netting twice both against Manchester City in the semi-final and Chelsea in the final.

But then he signed a new contract and things went a bit wrong. Just 16 months later, the club got rid of him because he'd upset Mikel Arteta. He joined Barcelona for free, then had a miserable time at Chelsea, but has revitalised a stalling career with Marseille.

Despite the rough end to his time at the Emirates Stadium, he's still remembered as one of the most impactful January signings.

8 Gary Cahill (Bolton Wanderers to Chelsea, £7m)

Cahill left struggling Bolton for Chelsea in January 2012, but he must have thought he'd swapped one crisis club for another when Andre Villas-Boas got the sack less than two months after he'd arrived.

But Cahill started to shine under Roberto Di Matteo and came into his own in the Champions League. He helped Chelsea pull off a dramatic comeback win over Napoli, knock out Barcelona at Camp Nou (after John Terry had been sent off) and then see off Bayern Munich in their own stadium to win the trophy for the first time.

But Cahill wasn't just a one-season wonder. He was also really important to Chelsea's league title wins under Mourinho and Conte. He won a total of eight trophies with the Blues and was named in the PFA Team of the Year three times. Not bad at all for £7m!

7 Kieran Trippier (Atletico Madrid to Newcastle, £12m)

When he left La Liga champions Atlético in January 2022 to join struggling Newcastle just weeks after the club's Saudi takeover, a lot of people were wondering what Trippier's motives were. And he had a nightmare debut as Cambridge United knocked his new side out of the FA Cup.

But Trippier has been a game-changer for Newcastle. He's been an inspirational leader, even after he got a bad ankle injury.

Once he'd recovered, he led Newcastle to the Carabao Cup final and their first Champions League qualification in 20 years. He's contributed to 25 goals for the Magpies, which is pretty impressive for a defender, and his experience and defensive skills have helped Eddie Howe's side become one of the top teams in the league again after decades in the wilderness.

6 Philippe Coutinho (Inter to Liverpool, £8.5m)

Coutinho saw Liverpool as a way out of a frustrating period with Inter, and it didn't take long for the Reds to realise they'd struck gold. He added real quality to Brendan Rodgers' side, and in half a season scored three times and set up seven goals. He was even better the next season, helping Liverpool come close to winning the title after forming a great understanding with fellow South American Luis Suarez.

He outlasted Suarez and Rodgers and became a crucial part of Jurgen Klopp's side, contributing to 62 goals under the German and briefly forming a mouth-watering attack known as the 'Fab Four' alongside Mohamed Salah, Sadio Mane and Roberto Firmino.

But then Coutinho got a bit too big for his boots and couldn't resist joining Barcelona in January 2018. But Liverpool got the last laugh, pocketing £142m ($178m) from his sale to fund Virgil van Dijk and Alisson, laying the foundations for future Premier League and Champions League wins. Coutinho had a rough time at Barca and is now finishing up his career back in Brazil with Vasco da Gama.