On January 27, 1970, U.S. Patent No. 3,492,131 issued to James M. Schlatter on Peptide Sweetening Agents (aspartame):

The U.S. Food and Drug Administration approved aspartame for use in certain foods in 1981, soft drinks in 1983, and as a general-purpose sweetener for foods and beverages in 1996. The European Union approved aspartame in 1994 as a food additive. It is currently approved for use in more than 100 countries.

Aspartame, like other artificial sweeteners, was discovered by accident when the researcher licked his fingers to separate some papers and noticed the sweet taste and investigated. Apparently to be successful in the artificial sweetener business, you have to be a little casual with personal hygiene, and a bit lax in laboratory safety procedures.