Tinker looks a lot like his twin- he wears the same tunic (except for when you change it), has the same hair style (though in a brown color), and also wears the same boots. The differences are that he is slightly taller, his nose is smaller, and his head is larger.
The Legend of Zelda: Spirit of Darkness
This is his first appearance. In it, he is the twin brother of Link and is the older brother of Saria. He joins Link and Reubell on their quest, and can be controlled by Player 2. If there is no Player 2, Tinker simply follows Link around and is relatively useless. He can do anything Link can do.
Tinker reappears in Super Smash Bros. Omega, as a recently announced Zelda series character, alongside Young Zelda. He uses the appearance shown above, wearing the Water Tunic instead of the Grass Tunic like his twin. Unlike Young Link (who takes on the same appearance as Link in LZSoD), Tinker is unlockable.