Doctor Who: Before There Was the Sonic Screwdriver There Was the First Doctor's Ring
There is one final aspect of the ring that may actually be the most telling about the origin of The Doctor. The Lance Parkin novel Cold Fusion explicitly states that the ring at one time belong to a figure from Gallifreyan history known as The Other. Who was The Other? According to Lungbarrow, which is probably the most important spin-off novel in all of Doctor Who, The Other worked alongside Omega and Rassilon in order to transform the Gallifreyans into Time Lords. However, though both Omega and Rassilon continued to influence history and were well-documented, almost nothing was known about The Other. It was even rumored that he may not have been Gallifreyan at all.
In Lungbarrow it's shown that the same feats that made them masters of time also caused the Time Lords to become sterile. No longer able to reproduce biologically, they developed genetic looms that would weave children from raw material. When Rassilon began to seize tyrannical power, The Other supposedly threw himself into one of the looms, awaiting the day of his reconstruction. It has been heavily implied that The Doctor is that reconstruction, especially when the First Doctor retuned to Gallifrey's founding to rescue the last naturally-born Time Lord, Susan Foreman, granddaughter of The Other.
And of course, he wore his ring.