Jamaican sprint great Usain Bolt and British distance legend Mo Farah will attempt to sign off with gold at the World Championships which begins in London on Friday.The pair, who have 28 world and Olympic titles between them, will both retire from the track by the end of the season.Elsewhere, Jamaica’s Elaine Thompson and Dutchwoman Dafne Schippers renew their sprint rivalry, while Britain’s Laura Muir will attempt a formidable 1500m-5,000m double.With Bolt not defending his 200m title, 400m world record holder Wayde van Niekerk will attempt to double up and establish himself as one of the new figureheads for the sport.I can emulate Bolt – Van NiekerkFellow South African Caster Semenya is also fighting on two fronts, stepping up to 1500m as well as attempting to regain the 800m title she won in 2009 and 2011. The Championships begin on Friday, five years to the day since Great Britain won three Olympic gold medals in less than an hour on ‘Super Saturday’ at the same venue.Bolt draws curtain on careerBolt’s 100m world record of 9.58 seconds came in the 2009 World ChampionshipsBolt originally intended to retire in the wake of Rio 2016. However he reconsidered that plan after his sponsor suggested a London farewell a year later instead.Now 30, the Jamaican had a slow start to the season, dipping under 10 seconds for the first time in Monaco a fortnight ago. Do you remember the first time you saw Bolt?He is only the joint-seventh fastest man over 100m in 2017, but has a history of rising to the big occasion.Only once in seven major 100m finals has Bolt failed to win gold, and that was after a false start at the World Championships in Daegu in 2011 took him out of the race.Coleman, one of Bolt’s foremost rivals, is still a student at University of TennesseeTwenty-one-year-old American Christian Coleman – who ran a world-leading 9.82 in June – a 35-year-old Justin Gatlin and 2011 world champion Yohan Blake may be Bolt’s biggest rivals for gold in the final on Saturday. Bolt’s final race before retirement is likely to be the 4x100m relay final seven days later. A homecoming farewell for FarahFarah’s 5,000m and 10,000m double was one of the defining memories of the London Olympics five years ago.Since then the 34-year-old has repeated the feat at World Championships in Moscow and Beijing as well as last summer’s Rio Olympics, and is favourite to do so once again before shifting his focus to marathon.However he is facing a crop of young pretenders with Ethiopian teenager Abadi Hadis the fastest this year over 10,000m and 23-year-old compatriot Muktar Edris leading the 5,000m time charts.Farah’s preparations have been at times sidetracked by questions over training methods however. Mo Farah won his first World Championship gold medal in Daegu in 2011Computer hackers released documents in July that showed Farah’s blood tests initially raised suspicion before later being cleared. His coach Alberto Salazar is under investigation by the US Anti-Doping Agency, while UK Athletics staff may have failed to properly record infusions of a controversial supplement given to Farah.Both Farah, who has refused to speak to newspaper journalists going into the championships, and Salazar have denied any wrongdoing.Farah’s 10,000m final headlines Friday’s opening day of competition with Wednesday’s 5,000m heats deciding the line-up for the final on Saturday, 12 August.Home Hopes Beyond Farah, Britain has more medal hopes than expectations.Muir broke Dame Kelly Holmes’ 1500m record at London Stadium last year, but found the pace of Kenya’s Faith Kipyegon and Ethiopia’s Genzebe Dibaba too hot to handle over the final 800m in a tactical Olympic final in Rio.Kipyegon and Dibaba are both in the field in London along with the Netherlands’ Sifan Hassan, who has the three fastest times of the year, and Semenya.British Athletics performance director Neil Black gave Muir only “a 1%” chance of adding the 5,000m to her schedule after she suffered a foot injury in June, but Muir is determined to pursue the longer distance after breaking the British indoor record in January.Katarina Johnson-Thompson will attempt to fill the void left by Jessica Ennis-Hill’s retirement in the heptathlon, taking on Olympic champion Nafissatou Thiam. Tom Bosworth broke the racewalking mile record in July and will aim to improve on his sixth-place finish in the 20km in Rio.