I don't think hes the biggest.. maybe the tallest?
I Googled it and found some neat info! (That's how bored I am at this hour of night)
The Guiness Book of World records:
The world's smallest dog living in terms of height is Whitney, a Yorkshire terrier who measured 7.6 cm (3 in) to the shoulder on November 26, 2002. Whitney is owned by the UK's Christopher and Patricia Sheridan of Shoeburyness, Essex, UK.
And the largest dog: "Hercules", an English Mastiff with a 38-inch neck and 282 pounds of pure dog.
He looks huge!