It has been the cause of a degree of controversy but Wales have at last reached number one in World Rugby's rankings.

It might have confused a few, including New Zealand coach Steve Hansen, and could prove a fleeting accolade with Ireland possibly toppling Wales with a victory over England this weekend.

It has been a rapid rise from February 2018 when Wales lost against Ireland in Dublin and dropped to seventh in the world rankings.

Eighteen months, a Grand Slam and 15 wins in 16 matches later, Wales are top of the pile with world champions All Blacks knocked off their perch for the first time in almost a decade.

BBC Sport Wales examines how Warren Gatland's side turned things around.

Six Nations success

Wales started the 2018 Six Nations with an emphatic victory against Scotland before away defeats against Ireland and England.

With no silverware to play for, Gatland made a bold call by making 10 changes for the visit of Italy, including a debut for flanker James Davies.

The option paid off with the much-changed side running in five tries in the 38-14 win, including two for George North.

Gatland made a further seven changes for France's arrival, knowing success would seal second place behind Grand Slam winners Ireland.

A Liam Williams try and three Leigh Halfpenny penalties gave Wales a 14-13 victory. The hosts dogged defence held firm for victory in a game that was far from a classic.

Successful summer

Most of Wales' 2017 British and Irish Lions were given a summer off for a Test South Africa and two-test trip to Argentina.

North and Ross Moriarty were the only original 2017 Lions selections included in Wales' 31-man party.

Cory Hill and Ellis Jenkins were co-captains, while Cardiff Blues scrum-half Tomos Williams was the only uncapped player.

Wales' second string beat a South Africa shadow side including seven new caps 22-20 in Washington DC. Victory was sealed with a late charge down by replacement hooker Ryan Elias.

In Argentina, Wales' young guns produced and beat the Pumas 23-10 in the first Test in San Juan.

Flanker James Davies scored his first international try, while North also crossed and Rhys Patchell kicked 10 points.

A 2-0 series win was secured by a 30-12 win in Santa Fe with Patchell notching up another 20 points in a composed performance, while wing Josh Adams produced a superb solo try.

The only negative was a late red card for number eight Ross Moriarty, sent off for a prolonged headlock on Pumas outside-half Nicolas Sanchez.

Unbeaten in November

Wales welcomed back their first-choice players for the November programme but had been rocked by the summer retirement of record captain Sam Warburton, while Lions number eight Taulupe Faletau was injured.

The visit of Scotland to Cardiff in November was unusual, but Wales claimed the inaugural Doddie Weir Cup.

The 20-11 win was based on tries from North and centre Jonathan Davies, playing his first Test for almost a year, and complemented by 11 points from Leigh Halfpenny's boot.

Next was attempting to halt Wales' Wallabies hoodoo. Gatland's side had not defeated Australia in 10 years with a losing sequence of 13 defeats.

This stranglehold was finally broken as Wales replacement Biggar's late penalty settled a nerve-shredding 9-6 win.

After kicking two penalties, Halfpenny was forced off the field following a dangerous challenge from Samu Kerevi that was to sideline the full-back for four months through concussion.

Biggar, who was starting his super-sub stint with Gareth Anscombe starting regularly at 10 in the winning Gatland reign, stepped up to slot the successful kick.

The Northampton fly-half was named man of the match in the next victory over Tonga as Wales won 74-24. Biggar was one of 14 changes that also included Liam Williams, who scored two tries on his 50th cap.

Just the Springboks stood in the way of the first-ever autumn unbeaten sequence and Wales achieved this feat with a 20-11 win.

Wales led 14-3 at half-time following tries for prop Tomas Francis and Liam Williams before Biggar again came off the bench to kick two late penalties.

The game ended on a devastating note as back rower and man of the match Ellis Jenkins left the field on a stretcher with a serious knee injury that has ruled the Cardiff Blues skipper out of the World Cup.

Grand Slam glory

Wales achieved their third Grand Slam under Gatland in 11 years and became the nation's most successful side by prolonging the winning sequence to 14.

The class of 2019 won games in a variety of different ways and showed remarkable fortitude on and off the field over a glorious seven-week period.

Everything started on a frenetic Friday night in Paris where Wales found themselves trailing 16-0 at half-time before launching a record comeback.

Wales were unrecognisable in the second half as North scored two tries and scrum-half Tomos Williams also crossed, while Biggar came off the bench to see out the victory.

From Paris to Rome and a much-changed Wales side equalled their record run of 11 successive Test wins with an unconvincing 26-15 victory over Italy.

Tries from Josh Adams and Owen Watkin, plus 14 points from Biggar, sealed victory.

So Wales knew victory over England in Cardiff would represent a 12th straight win and break a record winning sequence set in 1910 - and Gatland's side delivered with a stirring second half.

England led 10-3 at the interval but Wales came battling back with tries from Cory Hill and Josh Adams as replacement Biggar took control in the closing stages in a 21-13 win.

Celebrations were short lived as Welsh rugby politics took over with a proposed merger between regional sides Ospreys and Scarlets dominated the build-up to the game in Scotland.

Wales ignored the off-the-field controversy with a battling 18-11 away win against Scotland with tries from Adams and Jonathan Davies to set up a Six Nations day of destiny with Ireland.

A tough contest was expected against the defending champions, but Wales steamrollered their opponents 25-7 in the Cardiff rain.

After Hadleigh Parkes' early try, Anscombe kicked 20 points as Wales saved their most comprehensive display of the tournament for the finale.

Wales were never spectacular in attack but were clinical at crucial times.

It was their remorseless defence and remarkable resilience under pressure which clinched the title, led by inspirational leader Alun Wyn Jones who was named Six Nations player of the tournament.

Number one

Wales reached August 2019 knowing they would have opportunities to be ranked as the best side on the planet with their first chance coming in the opening World Cup warm-up against England at Twickenham.

But after Australia had opened the door with a thumping victory over New Zealand, Wales stuttered to a 33-19 defeat, bringing the 14-match unbeaten run to an end and Anscombe was also ruled out of the World Cup with a serious knee injury.

Six days later, and despite the All Blacks hammering the Wallabies in Auckland, Gatland's side did not fluff their lines in a hard-fought 13-6 win with North again crossing the tryline.

It was a 15th win in 16 matches and took Gatland's side to the top of the world rankings. How long they stay there, and most importantly, whether they will be top after the World Cup final in Japan on 2 November remains to be seen.

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