Four new head coaches, a raft of uncapped up-and-comers and a rivalry that stretches back more than 135 years.

The history, drama, thrills and spills of the Six Nations return this weekend to start the latest chapter in the world's oldest international rugby tournament.

In the wake of the Rugby World Cup, there are plenty of new characters, on the pitch and on the touchlines, to spice up the storylines.

Here is what you need to know about the 2020 tournament.

Wales

Thanks to the call of the British and Irish Lions, there have been a couple of caretakers, but it is 13 years since someone other than Warren Gatland was Wales head coach as they went into a Six Nations campaign,

Wayne Pivac has the intimidating task of following a man who delivered three Grand Slams, the latest lifted 12 months ago.

The New Zealander could have done without an injury that rules out centre Jonathan Davies, the 'captain' of the claustrophobically tight defence that characterised Gatland's reign.

Shaun Edwards, who masterminded that part of the game from the touchline, is also absent, having taken his inside knowledge to Six Nations rivals France.

But there are some welcome faces back on the scene. Scrum-half Rhys Webb is available after bringing a hasty end to his Toulon stint, while Taulupe Faletau, arguably the tournament's best number eight on top form, is hoping he is at the end of a two-year run of injuries.

Neither were part of a World Cup campaign that promised much but couldn't break new ground. Wales were squeezed out in the semi-finals by eventual champions South Africa, matching their best run at the tournament back in 2011.

One to watch: Louis Rees-Zammit: The 19-year-old wing has been one of this season's sensations, scoring 10 tries in 14 games for Gloucester. As the saying goes: If they are good enough...

Curveball: Coach Pivac is looking to box clever by convincing more Welsh-qualified, but English-based, players to commit to the cause. The recruitment of Saracens former England Under-20 centre Nick Tompkins and Wasps lock Will Rowlands shows he is having some success.

Title odds: 11-2

England

In the wake of the Rugby World Cup final defeat by South Africa in November, Eddie Jones entered, in his words, a "grieving process". He has since found a new challenge to reignite his passion.

"We want to be remembered as the greatest team that ever played rugby," he said in typically bold style.

England have some serious questions to answer before they can make any claim to that title.

Jones' 34-man squad features eight uncapped players but not a single specialist number eight to fill in for the injured Billy Vunipola.

At nine, Ben Youngs and Willi Heinz, 30 and 33 respectively, have limited shelf life and no clear successors.

And time is ticking on Jones himself, with his contract set to expire in August 2021.

But with Kyle Sinckler, Maro Itoje, Tom Curry, Sam Underhill, Jonny May and Anthony Watson all emerging from the World Cup well in credit, there is a confidence that might paper over those cracks.

One to watch: Ollie Thorley: Last season's Premiership young player of the year will have to fight for a spot, but is one of only three specialist wings in the squad and has the talent to take his chance.

Curveball: The Saracens saga. There may not be any ill-feeling from their team-mates, but the Sarries contingent come into the tournament with their club futures uncertain.

Title odds: 5-6 Fav

Ireland

Off the back of a Six Nations Grand Slam and a historic home win over New Zealand, Ireland finished 2018 as the northern hemisphere's pre-eminent team and the likeliest candidates to succeed the All Blacks as world champions the following year.

Instead that turned out to the high point of coach Joe Schmidt's reign.

A mediocre Six Nations campaign in 2019 was followed by a meek World Cup quarter-final exit in Japan.

Great Britain rugby league legend Andy Farrell served as an assistant to Schmidt and now succeeds him. He has gone for a similar strategy of evolution, rather than revolution, with his team.

Fly-half Johnny Sexton, once the firebrand young gun, now a 34-year-old senior statesman, is captain, with regular half-back side-kick Conor Murray keeping his place under severe pressure from Ulster's John Cooney.

However 95-cap mainstay Rob Kearney has been left out the squad altogether with the electric Jordan Larmour now undisputed first-choice full-back, while Leinster's rangy, roaming number eight Caelan Doris will make his debut against Scotland.

Can Farrell's tweaks restore the team to their 2018 levels?

One to watch: James Ryan: Leinster's flawless second row, still just 23, has long been earmarked as a future Ireland captain. With Rory Best no longer in the pack, he will be called up to take on some of the leadership burden.

Curveball: The tactics. Ireland under Schmidt were ruthless, accurate and drilled to parade-ground standard, rarely deviating from the head coach's kick-chase script. With former England maverick Mike Catt brought in as an attack coach, might things turn a little more free-form?

Title odds: 4-1

Scotland

The build-up to Scotland's campaign has turned into something akin to an episode of Love Island, dominated by rancour and rumour over the departure of a flamboyant main player.

Finn Russell, Scotland's mercurial fly-half, is believed to have hit the bar at the team hotel, ignored team-mates' advice to stop drinking, ignored his alarm clock for training the following morning and then declined to stick about when told he would be dropped for the team's opener against Ireland on Saturday.

Head coach Gregor Townsend insists that their relationship is still sound. Russell's social media 'likes' suggest that there might still be some issues to iron out.

Coupled with a knee injury to hot-stepping wing Darcy Graham and the disappointment of a Rugby World Cup campaign that failed to progress beyond the pools, expectations are not high.

However, the return of centre Huw Jones after a loss of form and flanker Hamish Watson after fitness issues are a boost.

And full-back Stuart Hogg, so long the heartbeat of the side and now the captain, sounds determined to drag more from his team-mates.

One to watch: Jamie Ritchie: The 23-year-old flanker was an age-grade star and is finally getting his run at senior level.

Curveball: The news that Scottish Rugby Union chief executive Mark Dodson was paid £933,000 in the last tax year will not have improved relations between blazers and tracksuits.

Title odds: 25-1

France

France's squad won't be measured by where they stand in March. Instead, coach Fabian Galthie has trained his sights very clearly on the 2023 Rugby World Cup, which his nation is hosting.

A 42-man initial squad featured 19 uncapped players and an average age of just 24.

It is not just blind faith in youth though. France's Under-20s have won back-to-back age-grade world titles. Romain Ntamack, son of former France wing Emile, made the step up to the senior Rugby World Cup side in the wake of winning the first.

One to watch: Antoine Dupont: A relative veteran with 20 caps and 23 years on the clock, the scrum-half is already one of France's brightest stars.

Curveball: Defence coach Shaun Edwards is a rare foreign appointment to the French coaching staff. Can he whip an erratic, inconsistent France into shape as he battles to get his tongue around the local lingo?

Title odds: 11-2

Italy

Yet another new head coach is in place. Franco Smith is keeping the seat warm until July, stepping in after Conor O'Shea quit to take up an administrative role with the Rugby Football Union.

The South African is the latest to try to close the gap on the other five nations. Italy have suffered whitewashes in four successive tournaments since they beat Scotland in February 2015, their last Six Nations success.

They will try to improve that record, for the most part, without Sergio Parisse.

The totemic number eight was denied the farewell he expected when Typhoon Hagibis caused the Azzurri's final Rugby World Cup pool match to be called off. The 36-year-old plans to be involved in at least one of Italy's home games during the tournament to put the seal on a career that has collected 142 caps.

One to watch: Jake Polledri: Born and brought up in the West Country, the 24-year-old Gloucester flanker qualifies for Italy though his grandmother and will be one of their go-to men in Parisse's absence.

Curveball: The Italian clubs have promised to give Smith more access and control over his international players. Could that produce a more coherence and consistency?

Title odds: 1,000-1