When the Doctor – with his big teeth and big, huge scarf and enormous ego – had the chance to rid the universe of the Daleks, he didn't hesitate. He touched the two wires together.
Sarah-Jane was shocked to see how the Doctor could so easily commit genocide even if it was the most evil race in the galaxy. She said that he had changed. He didn't think so but he didn't stop her from leaving. Harry went with her and the Doctor was sure they would lead a happy, boring life with lots of children – he couldn't care less.
When Romana kept the last piece of the key hidden from him, because 'no one should have this kind of power', he became furious. He exiled her to a harsh little rock with aggressive natives, because even in his anger he didn't want to kill something this beautiful – and besides a few decades might change her mind.
During his first visit Romana had become the natives high priestess and political leader.
On his second visit she had united them and brought them peace. The Doctor had to admit he was impressed.
On his third visit they had begun to develop a primitive science. She still refused to give him what he thought, but he was patient.
When he battled the Master his old friend told him, that he'd grown crazy. While Koshei himself was hardly sane, he didn't want 'his' Theta to suffer the same fate. He threw him off a tower, hoping the regeneration might bring him to his senses.
In the subconscious desire to show the world how harmless he was his body regenerated into a blonde, innocent-looking baby-face. When he opened the eyes and the Master saw into the soul behind the angelic features he fled.
On his fourth visit Romana had changed and the Doctor finally realized, where she had kept the piece of the key all the time and he laughed.
She might look like the princess with the piece buried inside herself, but exchanging a part of her soul for a part of the universe took its toll not only in appearance. This Romana was just a little bit mad.
She and him – they happily roamed the universe together: as heroes and villains, as saviours and demons and whatever they felt like.
In the end it couldn't work and he died – painfully – as his blonde innocent-looking counterpart poisoned him and fled with his TARDIS.
It took him one and a half centuries to get his hands on a time-travel device again and another 90 years to hunt down a TARDIS. He almost felt sorry when he took the Meddling Monk's last regeneration together with his transport.
His seventh self (which he regenerated into after a silly accident he refused to talk about) didn't feel any such qualms, when he killed a fifteen year old girl far from her own time and home to stop Fenric from ever rising again.
When he had fun with Morgana and Brigadier Lethbridge-Stewart got caught in the crossfire, he briefly remembered that he had known the man. He didn't lose any sleep over it.
His eighth face came about after the Master tried to turn him into a giant cat. He welcomed the feral aspects this brought to their relationship. And like a cat he was beautiful, elegant and absolutely deadly this time around.
While he enjoyed visiting the Master and giving in into some of his more primal needs they never travelled together. He enjoyed seducing and corrupting innocent young girls far too much.
Rose was easy – she would have done anything for the romantic stranger with his velvety locks and the aura of a bad boy. They never once looked back and she died 378 light years and 71,428 years from where she was born.
Martha immediately fell for him – but when she found out, that she wasn't a hero, but just some irresponsible guy having fun and damn the consequences, she almost found the strength to leave him. It took him quite some acting to convince her to stay. She eventually pulled the plug when he killed Donna, but what could you do?
He travelled, regenerated into a big bloke with a Northern accent and picked up a leather jacket and a cute red head. Together they roamed the universe, terrorizing the natives and the stupid little nurse, who followed her around like a puppy. They defied the will of the Time Lords, which were still nothing more like a bunch of old stiff-necked bores and they had the most fun imaginable.
The only real challenge they ever faced was, when a mysterious woman named River Song convinced Romana and the Master to work together to stop him.
author's note: This came about after watching 'Genesis of the Daleks', which basically is the beginning of the Time War back in Four's days. So what IF the Doctor had decided to kill the Daleks before they ever really existed? What kind of person would a Doctor be, that made this kind of decision?
Also I love the idea of Romana II and Five terrorizing the universe as much as Amy/Nine doing the same. I think the idea of Evil Doctor is disturbingly sexy.