AWS (IaaS) was started after Andy Jassy, who was Chief of Staff or Technical Assistant to the CEO at the time (2003/4), came up with a different vision for "Web Services" [0] to solve web-scale infrastructure problems every single project at Amazon then faced (and so, couldn't ship fast). That is, until Andy reinvented it, "Web Services" was simply limited to access to Amazon's catalog of SKUs [1][2]. As (may be) part of "Web Services" they also ran Target, AOL (shop@AOL), and toys-r-us' e-commerce stores [2]. Mechanical Turk showed up in 2004/5, S3 followed early 2006, whilst SQS, EC2 launched mid 2006 [3], and SimpleDB late 2007.
[0] https://youtu.be/9XTdhpYV168?t=457
[1] https://reference.wolfram.com/language/WebServices/tutorial/...
[2] https://www.informit.com/articles/article.aspx?p=99979&seqNu...
[3] https://web.archive.org/web/20210109135519/http://www.newsfl...