A Welshman invented the equals sign =

Robert Recorde was a Welsh physician and mathematician. In his 1557 book The Whetstone of Witt, he introduced the equals sign thusly:

And to avoide the tediouse repetition of these woordes: is equalle to: I will sette as I doe often in woorde use, a parre of paralleles, o: Gemowe lines of one lengthe, thus: == because noe 2 thynges can be moare equalle.

The scientist in me would have to quibble that parallel lines are not a priori equal in length (though perhaps Gemowe lines are defined as such), but in any case his innovation was eventually accepted and has been used for nearly half a millennium.

Credit to The New Shelton wet/dry for the info and Laputan Logic for the image.