GameShark is the brand name of a line of video game enhancers and other products for a variety of console video game systems and Windows based computers.
Currently, the brand name is owned by Mad Catz, Inc. who is actively marketing GameShark products for the Nintendo GameCube, Nintendo DS and Nintendo Game Boy Advance including the SP and Micro models. The GameShark products never have been licensed or endorsed by the manufacturers of the products that they work with. Originally, a cheat device that modified memory data, under the ownership of MadCatz the device has since become a dedicated game save storage device.
In The Legend of Zelda: Ocarina of Time, if you use the iron boots and blue tunic and sink Link down to the bottom of the pool in the labratory by Laky Hylia, a jail cell can be found containing a non-moving decal of a shark. It is assumed that this is Nintendo saying how they were against GameShark and other companies like it.