Three

From Relativespace

The Third Doctor is a renegade Time Lord from the planet Gallifrey. Once upon a time, he stole a TARDIS and left Gallifrey with his granddaughter, Susan. Since she left him he had other companions and explored the vast reaches of time and space. He grew old and regenerated, but continued travelling.

Finally, he found himself in a situation where he had to ask his own people for help. They did as he asked, but afterwards they punished him, wiping the memories of his companions and returning them to their own times. The Doctor was forcibly regenerated and exiled to Earth, where he attached himself to UNIT, becoming their scientific advisor alongside Dr. Liz Shaw and later, Jo Grant.

While he was working at UNIT, he solved a sticky problem for the Time Lords involving Omega and they released him from his exile. He started travelling away from Earth again, first with Jo and then with Sarah Jane Smith. Sarah was his companion at the time of his entry into Relativespace, though he is returning from Metebelis III alone.

Since he has been in the community, he has reacquired two of his three former companions, Jo and Liz. Sarah visits occasionally, but her fondness for his other selves prevents her from rejoining his team.