Not counting Grace, Ranji and Barnes (for some reason) :
There has been talk during the past few days about the rarity of undisputed boxing champions. Grace, Ranji and Barnes are among the few batsmen and bowlers considered the undisputed best in their own day. Undisputed meaning virtually everybody acknowledged them as the best at the time, with the period at the top being a minimum of a couple of years or so.
Other batsmen in this category before 1940 would be Trumper, Hobbs and Bradman. After that it becomes tricky as more countries produce high-class cricketers. My own view is that only four batsmen qualify since: Barry Richards, Viv Richards, Lara and Tendulkar.
Without trying to reignite the Barry Richards debate, the general perception between 1970 and 1975 was that he had no serious rivals, even if a few South Africans still preferred Pollock. In 1975 The Daily Telegraph selected its current World XI. Richards was first name on the teamsheet, opening with Barlow. Procter would have been picked had he been fit. Boycott was excluded from consideration because he had opted out of Test cricket. In England at least, the South Africans were still regarded as current internationals and it was thought they might be back soon. The Gleneagles Agreement put paid to that.
Any reservations about Richards were not about lack of Tests, but that he could get bored scoring easy runs and give his wicket away. Also that he was too fond of money. During the season in Australia he was on a dollar a run and averaged over a hundred. No gifting his wicket then.
Some English writers liked to divide up the 1950s between Hutton and May. Neither was undisputed leader for any length of time, with challenges from the Three Ws, Harvey and latterly Sobers.
Looking back now, many would give the 1960s in their entirety to Sobers. Some did then, but not everyone. As early as 1960-61, opposing captain Benaud said Kanhai was the world's best batsman. Several shared his view up to and including 1965. When Sobers pulled clear of Kanhai in 1966, another challenger had arrived in Graeme Pollock. At the turn of the new year in 1967, Pollock played an innings of 209 against Australia at Newlands entirely off the back foot due to injury. Reporting for The Cricketer, Michael Melford proclaimed Pollock the world's leading batsman and several Australians agreed. Bradman placed him ahead of Sobers.
Nobody since Tendulkar fits the bill. A few years ago six Sky Sports commentators debated the relative merits of the so-called Fab Four and couldn't agree. None placed Steve Smith first, not even Warne who went for Kohli. Botham put Smith last.
There seem to have been even fewer undisputed best bowlers during their own time. Perhaps only four: Spofforth, Barnes, O'Reilly and Lindwall.