With a very old breed like the Scottish Terrier, it's no understatement to say that their actual roots can be somewhat hard to pin down. Among all the terriers, those who fall under the category of Highland terriers in particular have much controversy surrounding just when and where they first appeared and who exactly was responsible. This stems from the unfortunate fact that for many years all of the Highland terriers were just simply called Skye terriers which today are their own particular breed that we recognize as being totally different from the Scottish terrier. There is some mention of Skye terriers that fit the description of a Scottie as early as the 16th century, but just which one came first and which descended from the other is still a matter of much discussion. Confounding the matter even further is the fact that Scottish Terriers and West Highland White Terriers are very closely related breeds, so close that in the past they were very frequently mistaken for one another, with many Westies being called "White Scotties" or Scotties being wrongly identified as "Black Westies".
With so many conflicting facts, what do we really know about the origins of the Scottish Terrier? What is known for certain is that by the 17th century, a breed that can be positively identified as the Scottish Terrier had taken up residence in England. In fact, James I was famously fond of the breed and often made presents of them to his contemporary political figures. Writings from the time indicate that knowledge of the breed was advanced enough to be trusted because important distinctions were openly made between the Scottish Terrier and the English Terrier, two very similar breeds.
Things began to clear up considerably in the late 1800s, when dog shows became popular and it was necessary to establish the objective standards by which a particular specimen of a breed could be judged. With this, it became necessary to finally split up the lump category of "Skye terriers" into its constituent breeds, which include many distinct breeds that we still see today, including the Scottie, the "true" Skye terrier, the Cairn terrier and the aforementioned Westie. Never one for having a clear, traceable history, however, the Scottie was still in certain regions known by a totally different name: the Aberdeen terrier.
It wasn't until four particularly distinct specimens of Scottish Terrier owned by a group of people in and around Aberdeen (Roger Rough, Tartan, Bon Accord and Splinter II) began winning a huge number of dog shows that the official pedigrees and standards that we know today were adopted and the history of the Scottie becomes clear.
Ultimately, largely due to their superficial similarities to other Highland terriers, it is unknown who was the first to develop the Scottish Terrier, or just when they first appeared. To many though, this simply adds to the charming character of an already unique breed.