So in effect most of the Doctors represent a different relationship.

01: Grandfather
02: Uncle
03: Father
04: Roommate
05: Big brother
06: Spouse?
07: Uncle
08: Best friend
09: Stepdad
10: Crush?

Most of them are pretty obvious and overt. Not really sure how to classify either Colin Baker or Tennant, though.

Colin Baker — there’s an element of that over-familiarity and antagonism from living with someone. Yet there’s a certain codependance. Similar to a roommate figure, similar to a father figure, similar to a sibling. Anyway: frayed nerves, underlaid by a certain intimacy. Strained affection. There’s a history here, yet the constant sense of obligation has taken its toll.

And Tennant is just — he seems to be the do-him-or-be-him guy. There’s a certain aspirational quality.