Both tours resulted in series victories for the Lions, with Davies playing a staring role from the back of the scrum.
Nicknamed 'Merv the Swerve', Davies was a superb all-round athlete who was equally comfortable in attack or defence. A Hard-runner and an aggressive tackler, Davies had the handling capabilities to link forward and back play and keep the Lions on the front foot against formidable opposition.
His abilities at the back of the lineout prompted New Zealand legend Colin 'Pine Tree' Meads to claim that the Welshman had the All Blacks 'donkey licked' during the Lions' only ever series win in New Zealand 37 years ago.
A previous World record holder for the most number of internationals cap as a No8, Davies played 38 times for Wales, without missing a match.
He led his country to Grand Slam glory in 1976 and was widely expected to captain the Lions on their tour of New Zealand in 1977. However, he was to be denied that honour as his career came to an unfortunate end in 1976 when he suffered a brain haemorrhage playing for Swansea in the Welsh Cup semi-final. Thankfully, although the injury brought his playing days to a premature conclusion, it stopped short of taking his life.
Mervyn Davies' factfile
Date of birth: December 9 1946
Clubs: London Welsh, Swansea
International caps: Wales 38
Davies' Lions lowdown
Lions debut: Versus New South Wales, May 15, 1971
Lions Tests: 8 (All four Tests in 1971 and all four Tests in 1974)
Lions non-Test appearances: 19
Total Lions appearances: 27 (14 in 1971 and 13 in 1974)
Lions points: 25* (5 tries) * under the current scoring system of five points for a try
Final Lions appearance: Versus South Africa, Johannesburg, July 27, 1974
Mervyn Davies (l) with fellow 1971 and 1974 tourist JPR Willkiams (r)
On earning a first Lions call up
"It was the greatest thrill of my rugby career receiving the letter inviting me to become a British Lion. It was the next step in my personal quest to be recognised as a great player, a step towards the ultimate goal of playing in a winning Test series against the All Blacks."
On that desire to win in New Zealand
"The world may have been a bigger place back in 1971, but some things don't change. If you want to be seen as a great rugby player you have to prove yourself on the toughest playing fields of all, New Zealand.
"I'd first met the All Blacks after Wales had won the Triple Crown in 1969 and we went, fresh-faced and innocent, to New Zealand and Australia. We thought we were quite good. We learned just how poor we actually were.
"But some thing changed for the Welsh players as we conceded two huge defeats Down Under. We returned vowing never to suffer such indignity and humiliation again. The Lions' tour of 1971 gave us the chance to prove we had learned from that bitter experience two years earlier and it was no coincidence that there were 10 Welsh players who figured in the four Tests."
On the fear factor associated with the All Blacks
"Being invited to be a Lion was a great feeling, but it also brought with it considerable fear. It may sound melodramatic, but the only comparison I can give to getting ready to face the All Blacks is likening it to going 'over the top' in World War One.
"So many of the All Black forwards were heroes of mine - Colin Meads, Ian Kirkpatrick, Brian Lochore and Ken Gray. They were literally giants of the game - and they were all waiting for us in New Zealand."
"So we headed for New Zealand feeling very much like Daniel going into the lion's den. There were 30 of us and a whole nation of them - no barmy army to give us comfort from the side.
"The task ahead of us was massive. The last Lions team that had been to New Zealand had been massacred in 1966 and we had 26 games ahead of us, 24 of which were in New Zealand.
"We had to become the first Lions team to win a Test series in New Zealand to achieve our dreams. Some people laughed at us for daring even to dream."
Davies (back row to right of shirt) at a recent celebration of Welsh Lions
On a miserable start to an historic tour in '71
"We left the south coast of England and headed to Australia. It took us 30 hours to reach Brisbane and two days later our dreams were in tatters. How on earth did we manage to lose 15-11 to Queensland?
"Weren't we supposed to be the best British team to leave our shores?
"The Aussie press had a field day with us and tagged us 'losers in the making' as we headed to New Zealand.
"I missed that first game and then helped steady the ship with a narrow 14-12 win in Sydney against New South Wales. It was not the sort of start we had wanted."
On the winning mentality that saw the Lions through Davies' arduous first tour
"The thing is that failure was not a word, or a scenario, that we were prepared to contemplate.
"We arrived with a job to do and we set about our task in impressive style by reeling off a number of heavy victories in our opening matches in New Zealand.
"We were the first breed of professionals with a small 'p' to come out of the UK and Ireland. We didn't consider the Lions tour to be a bit of a jolly - we wanted to go there and prove ourselves and win the series. We had genuine desire backed up by ruthless commitment, real determination and no little skill.
"We had to forget about wives, girlfriends and family commitments. Our only focus was what was ahead of us over the next three months. Rugby was no longer a part of our lives, it was our life.
"Everyone has this image of the 1971 Lions playing wonderful, expansive rugby throughout New Zealand, but the real truth was that the method wasn't important to us, it was just the result we wanted.
"We were well prepared, highly motivated and we rode our luck. Just like every other Lions side before us, we wanted to win - the real difference with us, though, was that we actually believed we could."