The term (Yorkshire) tyke is used as a nickname for a person from Yorkshire.

The noun tyke is from Old Norse tík, denoting a female dog (cf. Norwegian tik, female dog, female fox). The English word dates back to the early 15^th century; it denoted a dog, especially, depreciatively, a mongrel, and was applied to an unpleasant or coarse man. Because it was said in playful reproof to children, it came to also denote a small child, especially a cheeky or mischievous one.

The nickname given to the people from Yorkshire might have arisen from the fact that tyke was in common use for dog in that county.

Yorkshire tyke is first recorded in A New Dictionary of the Terms Ancient and Modern of the Canting Crew (London, 1699), by “B. E. Gent.”:

Yorkshire-tike, a Yorkshire manner of Man.

It is not possible to know from this dictionary definition whether the nickname was derogatory, but in The Wandering Pilgrim, published in London in 1740, by the English poet and diplomat Matthew Prior (1664-1721), the Yorkshire tyke exemplifies the poor:

But pass―The Æsculapian-Crew [= the physicians],
Who eat and quaff the best,
They seldom miss to bake and brew,
Or lin [= fail] to break their fast.

Could Yorkshire-Tyke but do the same,
Than He like Them might thrive,
But Fortune, Fortune, cruel Dame,
To starve Thou do’st Him drive.

The following, from The Gentleman’s Magazine: and Historical Chronicle (London) of May 1739, indicates that Yorkshire tyke was indeed pejorative. (Dick Turpin, born in Hempstead, Essex, in 1705, was an English highwayman. He was a cattle and deer thief in Essex before entering into partnership with Tom King, a notorious highwayman. In 1737, he moved to Yorkshire under the alias John Palmer. He was hanged at York for horse-stealing on 7^th April 1739.):

     Epigram on Turpin. By a Yorksh. Gentleman.
Full oft the South has sneer’d our Northern clime,
And horse-stealing been call’d a county-crime:
But now no longer we will bear such jokes,
This rogue is theirs; and we the honest folks.
Of knaves and fools we don’t say we have neither,
But knave and fool are seldom found together.
Our purer Northern air’s too sharp by half,
A Yorkshire tike has bit this Essex calf:
This dull-bred rogue has found it to his cost,
A fish out of its element is lost.

     Answer’d. By an Essex Gentleman.
When Turpin cruis’d near home, splendid he roll’d
In cash, and rings, and watches cas’d with gold;
Lean * Yorkshire chang’d the scene, his trade fail’d there;
In vain those roads he try’d above a year,
Till poverty reduc’d him to small beer.
What cou’d he do, in that dire starving case,
But take the trade peculiar to the place?
Turn Yorkshire tike and steal a horse or two,
So hang at Tyburn ’midst the jockey crew?
For boldest lion, if with hunger stung,
Will feed on carrion, mix’d with poison dung.
     * Turpin fled from London thither, to screen himself, but was bit by a tike, and dy’d of the Country Disease.

In The Great North Road: The Old Mail Road to Scotland (London, 1901), the English author and illustrator Charles George Harper (1863-1943) explained very clearly the ambiguities and complexities that have made the people from Yorkshire accept and even adopt as a term of self-reference the nickname (Yorkshire) tyke:

  (2^nd edition, 1922)
The Yorkshireman’s armorial bearings are wickedly said to be a flea, a fly, and a flitch of bacon; because a flea will suck any one’s blood, like a Yorkshireman; a fly will drink out of any one’s cup, and so will a Yorkshireman; and a flitch of bacon is no good until it is hung, and no more is a Yorkshireman! No native of the county can be expected to subscribe to this, but no one ever heard of a Yorkshireman objecting to be called a “tyke.”
A “Yorkshire tyke” is a familiar phrase. By it we understand a native of this immense shire to be named.  No one knows whence this nickname arose, or whether it is complimentary or the reverse. To be sure, we call a dog a “tyke,” and to describe any one as a dog is not complimentary, unless qualifications are made. Thus, the man who is insulted by being called a dog rather takes it as a compliment to be dubbed a “sad dog” or a “sly dog,” and, like Bob Acres, lets you know, with a twinkle of the eye, that on occasion he can be a “devil of a fellow.” [note 1]
By common consent, whatever its origin may have been, “tyke,” applied to a Yorkshireman, is taken in the complimentary sense. Indeed, the Yorkshireman’s good conceit of himself does not allow him to think that any other sense could possibly be intended. He generally prides himself, like Major Bagstock, on being “sly, devilish sly.” [note 2] That he is so, too, those who have tried to overreach him, either in his native wilds or elsewhere, have generally discovered. “He’s a deep ’un,” says a character in one of Charles Reade’s novels, “but we are Yorkshire too, as the saying is.” When tyke meets tyke, then, if ever, comes the tug of war. “That’s Yorkshire,” is a saying which implies much, as in the story of the ostler from the county who had long been in service at a London inn. “How is it,” asked a guest, “that such a clever fellow as you, and a Yorkshireman, remains so long without becoming master of the house?” “Measter’s Yorkshire too,” answered the servant.
It is a sporting—more especially a horsey—county. “Shake a bridle over a Yorkshireman’s grave, and he will rise and steal a horse,” is a proverb which bears a sort of testimony to the fact.

 

 

Note 1: This is an allusion to Bob Acres, a character in The Rivals (London, 1775), a comedy by the Irish playwright, satirist and poet Richard Brinsley Sheridan (1751-1816):

– Bob Acres. Why, you don’t wish me to kill him—do you, Jack?
– Anthony Absolute. No, upon my soul, I do not.—But a devil of a fellow, hey?

 

Note 2: In Dombey and Son (1848), by the English novelist Charles Dickens (1812-70), Major “Joe” Bagstock is a sinister old soldier who deliberately sets out to befriend Dombey to spite Miss Tox, who has turned cold towards him owing to her hopes of marrying Mr Dombey. Devilishly, he arranges the marriage of Dombey to his rival in hard-grained pride, Edith Granger.
He has the habit of talking of himself in the third person:

He’s hard-hearted, Sir, is Joe—he’s tough, Sir, tough, and de-vilish sly!