David Tennant appeared in his first full adventure as the Tenth Doctor in the 2005 Doctor Who Christmas special The Christmas Invasion, ten years ago tomorrow. 

The Christmas Invasion 

Rose and the newly-regenerated Doctor continue their adventures together in this Christmas Special episode. Christmas becomes a time of terror for Planet Earth, as the whole of mankind falls under the shadow of the alien Sycorax. Rose needs the Doctor's help, but can she trust a man with a new face?

David Tennant and Billie Piper star with Noel Clarke, Camille Coduri and Penelope Wilton. The episode was written by Russell T. Davies and directed by James Hawes. Music was written by Murray Gold, including the specially composed Song For Ten.