Kubrick's aliens

2001italia: 2001: The aliens that almost were

Here's a good article talking about all the trouble Stanley Kubrick (and Arthur C Clarke) went to in trying to come up with a credible cinematic alien for the climax of 2001.  

Of course, by not showing them at all, the movie suggests God-like mystery and power, which even goes beyond Clarke's so-called third law:  any sufficiently advanced technology is indistinguishable from magic.

It's just lucky that none of experimental aliens worked.