Dame Judi Dench. She has the perfect balance of humor and depth for the Whoniverse, I think. She’d be on, preferably, as an historical character being badass and awesome. Or as a contemporary character being badass and awesome, I suppose. Because the Dame is, utterly, awesome.
I’m fairly sure she would give Eleven some choice looks and zing some sassy one-liners at him, and Eleven would adore her and be a little afraid of her in exactly the right way. Plus I like to think Amy would look up to her a little and Rory would be properly leery, but would like her in secret from the very first.
Dame Judi! Dame Judi! My vote’s for Dame Judi!