This is David Tennant, the tenth Doctor, 2006-Present.
Tennant was born David John McDonald on April 18, 1971 in Bathgate, West Lothian. At the age of three, Tennant told his parents that he wanted to become an actor because he was a fan of Doctor Who. Do we believe that? Well, could be, 1974 would be the end of Jon Pertwee's shift and the beginning of Tom Baker. In fact he mentioned on a BBC talk show that the first Dr Who story he ever saw was "Planet of the Spiders," the story ending with the Pertwee to Baker regeneration.
From a science fiction point of view the stories have become much more sophisticated over the years. The early stories tended to be the Doctor and his companions being chased by big, slimey monsters. Now they're about alternate universes, black holes, and sometimes the devil. Big improvement.
The companions were also upgraded. The earlier ones were "screamers", i.e. their primary function was to wander around until the horrible alien monster snuck up behind them and tapped them on the shoulder after which they would let loose a shrill and very high decibel scream. The new ones don't scream any more and are getting into time, space, and alternate realities just like the Doctor.
David may have his most interesting Dr Who acting chores ahead of him in the next few stories. The Doctor now knows that his "Song is almost over" as the lady on the bus put it, and he seems to adopting Dylan Thomas' advice on how to handle that, "Rage, rage against the dying of the light." We'll see what happens when a Time Lord goes into rage raging mode. Probably nothing good, maybe we should move to another universe until this blows over!
David's contribution to the Doctor's character is to allow him to show a little emotion. Dr Who began as a kids show, so the BBC didn't want any lovey-dovey hanky-panky going on, but now its become an adult show (probably because all the kids who used to watch it grew up!) so the Doctor can show the feelings he has for some of his companions, particularly Rose, and his loneliness because he's the last of his race. It's as though the TV show itself started as a child, became an adult, then middle aged, and will eventually be old.