The Sixteenth Doctor is the first Doctor to appear in the series. Little known fact, he's actually The Seventeenth Doctor, but dosen't like to count the War Doctor ("The Warrior"). The Fifteenth (Sixteenth) Doctor got his own 2-Part Cybermen Story called: The Last Quest, which resulted in the regeneration Into this incarnation.
The Doctor always refers to his Seventh Incarnation, probalbly because the actor (G. Orlando)'s favorite Doc is the seventh. They will be together in Story 10, The Two Doctors.