In 1557, Welsh mathematician Robert Recorde did something down right ludicrous. Instead of writing out 'is equal to' like any other good mathematician, Robert had the ingenious idea of simply drawing two parallel lines on top of one another. His reasoning, as written in his work 'The Whetstone of Witte', was that two equal lines were the most equal things possible.

Robert wrote:

'And to avoid the tedious repetition of these words: "is equal to" I will set as I do often in work use, a pair of parallels, or duplicate lines of one [the same] length, thus: =, because no 2 things can be more equal'

So, thanks to Robert, he saved us all plenty of time and effort by simply drawing two lines on top of one another. His genius, however, would have no effect on my average performance in Mathematics at school.

https://www.mentalfloss.com/article/76342/retrobituaries-robert-recorde-inventor-equals-sign