Aspartame is an artificial non-saccharide sweetener 200 times sweeter than sucrose and is commonly used as a sugar substitute in foods and beverages. It is a methyl ester of the aspartic acid/phenylalanine dipeptide with brand names NutraSweet, Equal, and Canderel.

Aspartame was discovered in 1965 by James M. Schlatter, a chemist working for G.D. Searle & Company. Schlatter had synthesized aspartame as an intermediate step in generating a tetrapeptide of the hormone gastrin, for use in assessing an anti-ulcer drug candidate. He discovered its sweet taste when he licked his finger, which had become contaminated with aspartame, to lift up a piece of paper.

Perhaps not the brightest of moments for a scientist treading uncharted territory, but in hindsight, his lapse ultimately paid off when he realized the substance tasted sweet (and it didn't harm him). The result led to the accidental invention of aspartame, which in 1969 was referred to in the Journal of the American Chemical Society as a sweetener. 

After the FDA commissioner approved aspartame for commercial use as a sweetening agent in 1981, it was later marketed and distributed under the more familiar brand names including Canderel, Equal and NutraSweet. Aspartame was initially approved as a tabletop sugar substitute, tablet, and additive in cereal, drink mixes, and other products. By July 1983, the FDA had greenlighted its use in soft drinks.

According to mashed.com & Wikipedia