Verified answer

Who created the engineers isn't answered, this was a theme in the movie of who created who and then who had to create that.

He was working for Weyland to hel him find a way to prolong his life and was testing to see what the black liquid will do and if it's something that will help Weyland.

They never explain the creation of the engineers, as it is more a matter of science vs. faith. David does that to test what will happen.

http://www.imdb.com/title/tt1446714/faq?ref_=tt_fa...

That should clear up any questions you have.