Now known as a significant part of the now ubiquitous AR platform, the charging handle has an interesting history from the first ambidextrous design (mounted on the top of the AR-10, inside the charging handle) to its final multitude of iterations.
Leitner-Wise has posted up a great, compact history of the charging handle and its various versions. The post winds its way through original intent and configurations to ultimately settling on why they are moving towards a steel charging handle. If you can get past the tongue-in-cheek nature, Leitner-Wise has some great points on why they are going in the direction they are.
Hit the link to be taken to the blog post. Its a great 5-minute read, if you can tolerate or look past the sales pitch it ends up being.