Michael Phelps, 31
After watching him swim at the US Olympic Trials last month, one thing became glaringly clear: Michael Phelps is still Michael Phelps. The four years since he won eight medals in London and then retired have done little to dampen his appetite to compete. He looks fit and sublimely in control of his body ahead of Rio.
Even as the likes of Laslo Cseh and Kosuke Hagino have posted better times than the 22-time Olympic medallist in the last two years, Phelps's big-stage presence coupled with that impressive tenacity to win means that he'll start as the favourite in the three individual events he has qualified for.
At the trials in Nebraska, Phelps won gold in all three events - 100m butterfly, 200m butterfly and the 200m individual medley - beating long-time rival Ryan Lochte by 0.31 seconds in the last of these events. While Cseh and South African Chad le Clos will rival Phelps in the butterfly events, the medley will see him face-off against Lochte and Hagino - two swimmers who have beaten him in the past. Yet, there will be little surprise if Phelps goes back home with three more Olympic gold medals.
In a scandalous year afflicted with outlandish conspiracy theories and abhorrent doping scandals, the world really wants Usain Bolt to win in Rio. For once, athletics watchers need somebody to reinstate their faith in a sport that was once populated by just clean athletes. And, Bolt can provide exactly that tonic.
For someone who has run so little in the last year and been hampered by a hamstring problem recently, Bolt's serene sweep to line in the 200m at the Anniversary Games was more about muted relief than anything else for the fans. It wasn't the quickest but it was efficient and effortless - a dangerous indication for his rivals that the burly Jamaican looks adequately prepared for Rio.
Several former athletes, including Michael Johnson, believe that a fully-fit Bolt will win gold in both the 100m and 200m, regardless of how good the others may seem right now. The 100m - with Justin Gatlin, Yohan Blake and Travyon Bromell - will be a difficult field to thwart even for Bolt. But the 200m, his pet race over the years, is almost certain to witness a comfortable Bolt win.
Ashton Eaton's win in the decathlon at the American trials earlier this month did not see him set any new world records, but it was the kind of breezy performance that actually made you wonder if Eaton could at all be touched in his quest for a second straight gold medal at the Olympics. In an event as rigorous as the decathlon, Eaton has time and again confirmed his status as the most complete athlete in the world, silencing the cynics along the way.
Before the 2015 World Championships in Beijing, there was some apprehension about Eaton defending the crown he had won so convincingly in Moscow two years prior.
But Eaton comprehensively outplayed the rest of the field, setting a new record.
The finest American decathlete since Caityln (then Bruce) Jenner, a repeat performance in Rio will see him match the great Daley Thompson.
In the run-up to the Anniversary Games in London last week, Mo Farah had just one aim: to run the 5,000m in under 13 minutes. When most athletes treat all competitions prior to the Olympics as mere warm-up events - showing scant regard for manner of victory - Farah's pre-race objective was a telling statement of intent.
With the pace waning and the rest of the field slowly fading away inside a stuffy Olympic Stadium, Farah set off on an astounding five-lap solo run. His finishing time: a quite remarkable 12:59:29. His fastest time at the distance since June 2012, Farah - even at 33 - looks fresher than ever.
Here, the lack of competition was a minor criticism; the time, however, a major throwing down of the gauntlet. Only one of those peculiar off-days can prevent the Brit from winning a second consecutive Olympic gold in both the 5,000m and 10,000m. Any doubts around who is the greatest middle-distance runner of this generation - Farah or Kenenisa Bekele - is likely to be settled in Rio.
You just do not mess with Valerie Adams. Earlier this month, Adams took to Twitter to rip apart an airport official in Monaco who had said a few insulting things about her in French, thinking that the shot-putter did not know the language. Much to his amazement, Adams is fluent in a number of languages, including French.
Just a few hours later, Adams competed at a Grand Prix meet in Budapest, giving a befitting reply to anyone who messed with her there too. Adams threw a season-best of 20.19m, storming her way to gold. Before her somewhat unpleasant exchange at the Monaco airport, Adams had thrown 20.05 at a Diamond League meet there - the first time she had crossed the 20m barrier since undergoing shoulder surgery earlier this year.
More importantly, her win in Budapest saw Adams beat her main rivals: American Michelle Carter and Germany's Christina Schwanitz. A third consecutive shot put gold in Rio looks like a mere formality.
There is no shame in admitting that most of us missed Jessica Ennis-Hill while she was away for two years after giving birth to her first child. That memory of her going past Tatyana Chernova on the home stretch of the 800m to ensure heptathlon gold in London four years is undoubtedly one of the most iconic shots in British sport.
Four years later, Ennis-Hill will not start as the overwhelming favourite in the heptathlon, but will easily be the most watched athlete during the Games. After winning at the World Championships in Moscow last year, Ennis-Hill confessed that she had surprised herself by clinching gold. In Rio, however, expectations from Ennis-Hill will be high.
The affable Sheffield native’s duel with the much younger Katarina Johnson-Thompson will be one to watch. Johnson-Thompson has been plagued by bouts of inconsistency and erratic finishes in the past, but she remains a sturdy challenger who brings with her the ability to startle.
It's not every day that you find a footballer on an "Olympic athletes to watch" list. When a silver-haired Lionel Messi and the rest of the Barcelona squad met up for pre-season training at the sprawling St George's Park facility in Staffordshire, Neymar was thousands of miles away training with the Brazilian Olympic squad. In fact, he missed his country's shambolic Copa America campaign owing to his Olympic commitments - a strong signal that the South Americans are taking the Olympics seriously.
In London four years ago, Brazil finished with just silver, losing to Mexico in the final. But this time, with a partisan home crowd behind them, Neymar and Brazil will start as favourites for gold. Neymar enjoyed yet another prolific season with Barcelona, winning the league and combining immaculately with Messi and Luis Suarez yet again.
More than gold, the home side will be looking to obliterate the harrowing memories of the 2014 World Cup, where they were hammered 7-1 by eventual champions Germany in the semi-final on home soil, in Belo Horizonte.
There are times you wonder if Chris Froome is actually human. The ease with which the Brit sauntered to a third Tour de France victory - despite a dangerous crash during the latter phase of Stage 19 - confirmed his status as one of the finest cyclists of this era.
A win in the Olympic road race and time trial will see Froome become the first man to win the Tour and the two Olympic events in the same year. In 2012, Froome's compatriot, Bradley Wiggins, won the Tour and the Olympic time trial, losing out narrowly in the road race. Wiggins himself has come out and backed Froome, saying that going purely by form, it will be difficult to look beyond Froome in both events.
The 60-km time trial will see Froome start as favourite in a field that will be devoid of his main rival, Tom Dumoulin, who injured himself in a terrible clash during the Tour de France.