"Like I said my name is Slade Wilson....I am skilled in nearly every martial arts. I can use almost any weapon. I have killed many people and fought powerful beings....I have skills far above a normal human.." Slade said "And now you Doctor.."

The Doctor looked at them all seriously. He said "Okay then. That's what I'll do. I'll tell you a story. A story of a mad man in a blue box. I hope you can believe this Because I've lived a long life...over 2000 years. And I've seen a few things. I walked away from the last great Time War. I marked the passing of the Time Lords. I saved them from that very war! I saw the birth of the universe and watched as time ran out, moment by moment, until nothing remained. No time, no space. Just me! I walked in universes where the laws of physics were devised by the mind of a madman! And I watched universes freeze and creation burn! I have seen things you wouldn't believe! I have lost things you will never understand! And I know things, secrets that must never be told, knowledge that must never be spoken! Now is that enough for you to trust me Wilson!" The Doctor then went to the console. The TARDIS Camera caught sight of Romulus.

(I did take this from the speech in Rings of Akhaten. I just thought it fit the moment)