As his father was World Rally Champion in 1990 and 1992 it is hardly surprising that Carlos Jr stepped into 4 wheel motorsport.
At 7-years-old he began to drive karts at his father's indoor karting centre in Madrid, but he only started to compete seriously in the summer of 2005 when he was 10. Over the next few years he gained a huge amount of experience and success in kart races across Europe.
By 2009 he was very much a talent to be reckoned with even though he had yet to turn 15. That same year he won the famous Monaco Kart Cup as well as the Western European region of the KF3 series covering England, France, Switzerland, Portugal, Andorra and Spain.
For 2010 he was invited to join the Red Bull Junior Team, contesting the Formula BMW European Championship and taking part in three rounds of the Formula BMW Asian-Pacific Championship with the Antonio Ferrari's Eurointernational team, thereby winning the Rookie Cup Formula BMW European Championship. A single race highlight was victory at the notoriously difficult Macau by 4 seconds in the Formula BMW Asian-Pacific Championship.
In 2011 he moved up to Formula Renault 2.0 and won the Northern European Cup with a superb 12 race wins and a total of 26 podium appearances through the 34 races. In the Eurocup he finished 2nd overall.
2012 saw the Spaniard step into the intense cauldron of the British Formula 3 Championship as a member of the legendary Carlin Motorsport team. His schedule was quickly expanded to include the Formula 3 Euro Series and then the tardily announced FIA European Formula 3 Championship which drew its points from some races from each of the other series.
It was a busy season and Sainz had some great races, there was the win at Francorchamps in a typical Spa downpour, a total of 4 wins in British F3 on his way to 6th in the championship. He was 9th in the Formula 3 Euro Series and 5th in the FIA European Formula 3 Championship. Youthful exuberance, inexperience and some misfortune cost him better championship placings.
In GP3 for 2013 he was teamed with fellow Red Bull Junior Daniil Kvyat in the MW Arden squad. The pair were frustrated early on with set up problems that confounded their attempts to make the tyres last the races. As that got sorted out the pressure was on to make up ground in the championship and while Kvyat eventually took the title, a mixture of some atrocious luck and and overly intense desire to finish in front thwarted the Spaniard. Tenth for the year was not a just reflection of his ability. He had far more fun in his Renault 3.5 outings and was happy to have that as his sole class for 2014.
The challenge for 2014 was to win the Formula Renault 3.5 championship and the 19-year-old was up to the task. Now with DAMS, his weekend at the season opener in Monza resulted in mixed emotions. He finished 18th in the first race but won the second. He left Monza with 25 points already in the bag, beating his previous entire season's score by 3 points already.
Another win at Aragon meant he doubled his score and in race 2 he finished 4th. Another 4th place followed at the one race weekend in Monaco. A perfect weekend at Spa followed with another 2 wins in the bag.
Moscow followed and 14th and 6th meant he only took 8 points from a possible 50. At the Nurburgring, he drove superbly in race 1 to win but in race 2, he retired. In Hungary, he was no match for Roberto Merhi who drove a fantastic race to lead by an astonishing half a minute from the rest of the field in the wet. In France, he drove two fantastic races to win and score a total of 50 points to extend his championship lead over Mehri, finally wrapping up the title at Jerez.
As part of his reward for winning the Formula Renault 3.5 title, Carlos tested for Red Bull at the post-season test in Abu Dhabi, the youngster having previously tested for both the Austrian outfit and its sister team at Silverstone in 2013.
Three days after the Abu Dhabi outing Carlos was named Max Verstappen's teammate at Toro Rosso for 2015. Not for the first time, Toro Rosso's hiring and firing policy has raised eyebrows, especially as the team would be fielding two rookies in 2015 with an average age of just under nineteen.
Assuming Max Verstappen was replacing Daniil Kvyat, Carlos must therefore have been replacing Jean-Eric Vergne. Which seems about right, because the Spanish youngster appeared to inherit the Frenchman's extraordinary bad luck, certainly in terms of reliability.
Whilst Verstappen, quite rightly, got the media adulation, the final standings and points score doesn't do Carlos justice.
Fact is, 2015 has to be observed from two angles; the car (the STR10) and driver line-up. Whilst one failed, the other succeeded.
Though the car was good - its one-lap pace particularly impressive - reliability was a serious concern, mainly in terms of the Renault power unit in the back.
In terms of qualifying, the duo were fairly evenly matched, Carlos leading the way 10-8. However, the Spaniard's 7 DNFs to the Dutchman's 2 tells another story, poor Carlos suffering all manner of issues, usually relating to the power unit.
Qualifying 8th for his maiden race, the Spaniard brought the car home in the same position next afternoon, despite an agonisingly long pit stop; not a bad start for someone who had never seen the track before.
Clearly fired up by his home crowd at Barcelona, Carlos put the car an amazing 5th on the grid, finishing ninth next day having made short work of his teammate.
Next time out, at Monaco, despite a (weigh bridge) penalty which saw him start from the pits, adapting a strategy that saw him complete 66 laps on one set of tyres, the determined youngster took a sole point for tenth.
At Austin he finished a strong seventh - his best result of the year, despite a 5s penalty, but sadly those were his last points of the season.
There were mistakes, most notably his determination to make friends with the walls in Singapore, yet there was also his resilience in climbing into the STR10 in Russia, following his horrendous qualifying crash.
Overall, looking back at that long streak between Austria and Belgium when the youngster suffered four consecutive DNFs, it would be wholly wrong to try and compare Carlos with his teammate, even though it is clear Verstappen is something special.
The move to Ferrari power - albeit a 2015 unit - for 2016 hopefully meant more reliability and race pace which meant we should witness even more improvement from the pair and thereby a better basis on which to compare them.
Sadly, due to the shenanigans of Daniil Kvyat in Russia and the unforgiving nature of Red Bull Motorsport consultant Helmut Marko, we were pretty much unable to directly compare Sainz and Verstappen in 2016.
After just 4 races the Dutch teenager was promoted to Red Bull while Kvyat found himself back in Toro Rosso overalls.
While we were unable to compare Carlos with Verstappen in 2016, and Kyat spent much of the season in the Twilight Zone, for much of the year it was clear that in the Spaniard Red Bull has discovered another true talent. Indeed, Red Bull is spoiled with riches.
Ignoring the fact that for much of the year Carlos' benchmark teammate was essentially a broken man, the fact is that the Toro Rosso-Ferrari package though initially strong became less and less competitive as the season wore on. Yet someone clearly forgot to tell Carlos.
On a regular basis the Spaniard, much like his countryman at McLaren, performed miracles in the STR11, providing 46 of the Faenza team's 63 points.
In the few races where he was partnered by Verstappen, the Spaniard gave a typically good account of himself, though in Bahrain and Russia he was the innocent victim of others' over enthusiasm. Indeed, while the youngster often suffered at the hands of others, only in Canada, where he crashed in qualifying, was he the architect of his own demise.
While Verstappen was (rightly) grabbing the headlines at Barcelona, Carlos came home a strong sixth, having run as high as third in the opening laps.
It was a couple of botched pit stops that wrecked his hopes of a podium in Monaco, while despite an engine failure in Austria which saw him fail to make it to Q3 he drove another convincing race to finish eighth.
Sadly, as the season wore on and the car became less competitive, reliability was also an issue, a sure-fire points finish in Singapore being thwarted by an MGU-K failure.
While the sixth in Brazil owed a little to the conditions, the Spaniard unlucky not to claim a podium, his drive to sixth in Austin just a few races earlier was one of the true highlights of the year.
It's worth noting that while we understood Kvyat's 'twilight period' following his demotion, there was no such behaviour from Carlos who had every right to feel aggrieved at Verstappen getting the Red Bull drive. Instead the Spaniard kept his head down and got on with it.
With Toro Rosso returning to Renault power in 2017, if the Faenza team could give him a good car, Carlos was sure to make more people sit up and notice his obvious talent.
Having clearly inherited his father's genes, Carlos excels in difficult and changeable conditions, and this was obvious at a number of races held in such conditions in 2017. In China and Singapore not only was his driving masterful, so too was his strategy, particularly in terms of tyres.
At Shanghai, he was one of the only drivers to start on slicks, and though initially it looked to be the wrong choice it eventually paid off. Then in Singapore he opted for Inters when others went full wet, eventually giving the Faenza team its best result since Sebastian Vettel's win at Monza in 2008
However, there were mistakes also, not least Bahrain where he took out Lance Stroll, subsequently eliminating the other Williams driver in Canada. Then there was the needless first lap crash in Japan, his final outing with Toro Rosso.
Nonetheless, with Daniil Kvyat having another of his erratic periods, Carlos was the main breadwinner for the team, contributing 48 of its 53 points.
Behind the scenes however, with Red Bull looking to lose Renault power at the end of 2018, moves were afoot to find a new engine partner for Toro Rosso. Eventually, having initially agreed a deal with Sauber, Honda opted to throw its lot in with the Faenza outfit.
However, as part of the deal to release Toro Rosso, the Italian team was forced to loan Carlos to Renault for 2018, though the Spaniard actually made the switch in time for the race in Austin.
Despite limited running in the RS17, he brought the car home 7th, scoring just two points less than Jolyon Palmer had managed in the previous 15 outings.
Though steering issues and a loose wheel saw him retire from two of the final races, from the moment Carlos arrived at Renault, the team, and teammate Hulkenberg, appeared to receive a much needed boost.
Assuming Renault could offer him a package with which to further prove himself, Carlos could set himself up nicely for 2019 when a number of contracts were up for grabs, not least the seat alongside his former teammate, Verstappen, at Red Bull.
Though Carlos finished the season tenth overall, 19 points adrift of his teammate, 2018 wasn't too bad a season for the Spaniard, and, unlike his teammate, he kept it on the black stuff.
Though never quite on Hulkenberg's pace, the Spaniard at least had consistency, scoring points in 12 races and giving Renault its best result of the season when he finished fifth in Azerbaijan, though his teammate subsequently matched this in Germany.
Unlike his teammate there were just two DNFs, and one of these an accident in which the hapless Spaniard was the victim of Grosjean (Silverstone).
Furthermore, in Hungary he gave the French team its best qualifying result of the season when he put the Renault fifth on the grid.
Unable to capitalise on his superb qualifying performance in Hungary, days later Carlos learned he was surplus to requirements at Enstone after Renault confirmed that it had secured the services of Ricciardo. However, rather than being welcomed back to Red Bull to re-partner with Verstappen, Carlos found himself heading to Woking to replace countryman Alonso.
In all honesty, at such a difficult time for McLaren, Carlos has his work cut out. The team not only appears to have lost its way technically, but also appears to have lost its direction in terms of leadership.
Indeed, Carlos could be on as hiding to nothing, for if things go well - which is doubtful - it will be claimed that McLaren has turned things around, while if things continue to deteriorate the Spaniard could well find himself bearing the brunt of it all.
All things considered, Renault, like Ferrari, may have gone the wrong direction in driver choice, and might well have been better served by partnering Ricciardo with Carlos.
Only time will tell.