That is a really good question, and one we've argued over in JDs for years. After much thought and discussion, my honest answer is... I don't really know!
Some people would say that anyone who played in any of our three winning Cup Finals would automatically qualify - I don't agree. I would say any of the players who played in both '52 and '55 would qualify by default, but what I would say of the 1991 Cup-Winning team (don't know a lot about the players from the fifties!) is that there was a few guys in there who are, to me, journeymen - including two of the goalscorers in the final! I mean no disrespect to these guys when I say that - I'd be delighted to buy any of them a pint should the opportunity present itself but, to me, legend is a word reserved only for the very best.
Dougie Arnott - cup-winner, played in the seasons we came 2nd and 3rd, scored loads of memorable goals against the Old Firm, length of service and one of our own. These things all go in his favour. To me, each of those things make up the criteria of a legend, and I think people can argue over how many of those things you need to be one. The fact that Dougie ticks all of those boxes is the reason he is my all-time favourite player. Guys like Martyn Corrigan only really get a tick in the length of service box and even then it was three years short of Arnotts spell. I think the Kaiser was absolutely magic and one of my favourites from recent years, but I'm afraid he doesn't deserve to be in the category of 'legend', and suggesting he does only cheapens the title for me.
However, that's just my opinion - it's very much open to interpretation!