A/N: Some companions that crossed regenerations (for example: Ben and Polly) may be listed with either their first or second Doctor...
The Alzarian mathematical genius from E-Space who stowed away. Sometimes I saw a bit of myself in you. You wanted to be taken seriously, to realise that you had valuable input. You wanted to be an adult, but you couldn't help being just a child. Nyssa and Tegan did like you, as if you were an annoying younger brother. You didn't see how upset they were when you died. You sacrificed yourself for your mathematics, which was somehow rather fitting for you. We all took you seriously then. None of us ever knew if you were right in the end.
I always felt very responsible for you. Because of your association with me, or rather the Master, you lost your step-mother, your father and then ultimately your entire planet. Despite so much loss, your care and compassion for others outweighed all the circumstances we found ourselves in. Your scientific curiosity took you far. You grew up while we travelled together and eventually after being infected with Lazar's disease, you took up the cause and elected to stay behind to make a better life for the other people infected. You knew there had to be a better way, and there was.
You always talked a good game, but there were very few you let see past that. You always had a large heart. Granted, a large mouth to go along with it too. I always felt guilty that you got lost in the TARDIS that first time, but I was thankful for the way our friendship progressed. You saw many things in our travels, but ultimately, it was the massive loss of life caused by the Daleks that finally pushed you to your limits. I hated the way we parted, but you have to know I only wish you the best.
A prince of Trion, yet you passed yourself off as an Earth bound schoolboy. You had an ulterior motive when you joined the TARDIS crew and tried to kill me. Granted, you were being coerced by the Black Guardian, but we soon rid you of that influence. Whether you ever admitted it or not, you were much older than the human teenager you pretended to be. No one could blame you that once we got back to Trion and you realised your family had been pardoned that you wanted to stay. Sometimes, home is truly the best place to be.
An American botany student, your love for life was matched only by our ability to argue. While all in good fun, sometimes I know we got on each other's nerves. I still wouldn't trade our time together for anything. You balanced that version of me more than any other companion could have. I hate how we parted, because ultimately, I never knew what happened. A huge part of me was afraid you died, and another part of me worried about you staying with Ycarnos. I only wanted you to be happy, and being a warrior queen didn't seem to suit.
A computer expert by vocation, but you could scream like no one's business. I never had to worry about not knowing when you were in trouble. The details of our meeting are sketchy, with that whole trial business going on at the time, but once we met, it seemed as if I'd known you a long time. I think you liked me better after my regeneration, at least you never made me work out again on that exercise bike. I still can't stand the taste of carrot juice. I don't quite understand why you left with Glitz of all people.
You called me Professor more than you ever did Doctor. Our relationship was the ultimate in student-teacher, or even parent-child. You had the ability to be so much more than your Earth teachers gave you credit for. Sure, you had a knack for faulty timing on your explosives, but you rarely showed fear and stayed the course. I pulled strings with your history and played with your future. Time willing, I would've petitioned for you to join the Academy. You could've been a Time Lord, until circumstances pulled you away to another war. Were you even human at the end?