They were the same, but they were different. Nevertheless, I've died for one and would gladly die for the other – if only I were able.
My name is Jack Harkness. Captain Jack Harkness, that is, and I am a prisoner on the Valiant, an aircraft carrier under the control of the Master, formerly known as British Prime Minister Harold Saxon.
How did I get in this mess? Well, that was the Doctor's fault. But I don't blame him – I never could.
The first Doctor I met was hard to crack. He quickly labeled me a conman and was convinced I couldn't – or wouldn't – change. I think I proved him wrong, though, by willingly taking that bomb onto my ship and almost sacrificing myself. But, he saved me – at Rose's insistence, I'm sure. Still, he saved me – he came back for me. From then on, I believe that there was an amount of grudging respect and admiration – at least on his part. By that time, I already cared for him a great deal.
When I faced those Daleks, it was with the knowledge that I was going to die. Still, I couldn't regret my death, for I'd bought the Doctor time – hopefully, it was enough. Also, we'd kissed (and what a kiss!).
Imagine my surprise, then, when I found myself breathing again. It was only later – once I'd met the current Doctor – I discovered that my immortality was thanks to Rose. Despite my dismay, I couldn't find it within myself to place the blame on her. She'd been acting to save the Doctor, and it was only an accident that she resurrected me.
Now, the present-day Doctor, the one I'm currently chained up for – if possible, he's even more mysterious than his predecessor. Truth be told, this one scares me a bit. He seems colder, and is less willing to forgive.
No matter – though the face may change, the man's essence remains the same. And it is that man – that Doctor – that I love and would lay down my life for.