The Computer Mouse was developed by Douglas Engelbart at SRI (Stanford Research Institute) International's Augmentation Research Center along with William 'Bill' English, his lead computer engineer.
Douglas filed for a US patent on 1967-06-21 and the patent US3541541 was issued on 1970-11-17.
This patent is the first patent which introduced a 'Computer Mouse' to the world.
Of-course the gadget wasn't called a mouse in the patent, it was called a X-Y POSITION INDICATOR FOR A DISPLAY SYSTEM. The name 'Mouse' was later coined owing to the wire coming out from the gadget resembling a tail of a mouse.
Engelbart's Patent for Mouse had been filed in 1967 but he released a demo of the invention in 1968.Just a few weeks before the demo of Engelbarts's mouse, German company Telefunken published on their early ball mouse, called "Rollkugel", on 2 October 1968. However, Telefunken did not apply for a patent.
This model of telefunken was the first ball mouse to be ever produced.
Just a few years later in 1972, Bill English, lead engineer of Engelbart's original mouse, created another ball mouse while working at Xerox PARC.
Later many innovations in mouse design and working took shape in the form of laser mice, wireless mice and so on. However, Douglas Engelbart's Mouse was the first Mouse ever. The patent US3541541 is the basic or the original patent for a 'Computer Mouse'.
References
[1] http://www.heise.de/ct/meldung/Auf-den-Spuren-der-deutschen-Computermaus-216255.html
[2] http://www.oldmouse.com/mouse/misc/telefunken.shtml
[3] http://www.oldmouse.com/mouse/
[4] http://inventors.about.com/library/weekly/aa081898.htm