So who had an aura - that difficult to define "something" that made a player stand out from the rest?
Ivan Lendl was one - he dominated tennis in the 80s and was regarded as a machine in some quarters - and one that was incredibly tough to beat.
Borg was another - his coolness and tendency to say very little gave him something extra.
Federer is another - during his period of absolute and unchallenged domination from 2004 say to 2006/07 his results were such that I think many lesser players simply didn't believe they could win - they were beaten before they took to the court.
Any other nominations?