Paula Radcliffe is up there but I don't know about the greatest.
Nice XC performances but that's not an Olympic event.
She has a WC Silver at 10,000 and a WC Gold in the marathon.
And of course the great world record in the marathon.
Moses Kiptanui has 3 WC Golds, 1 WC Silver and an Olympic Silver.
He ran the first sub 8:05 steeplechase with an 8:02. He then went on to be the first under 8 for the steeplechase.
He broke Said Aouita's 3000m open record. He broke Gebrselassie's 5000m world record before Geb smashed his mark back.
That is one serious running resume except for the missing Olympic Gold medal.