You may remember that the titular xenomorph in Ridley Scott's 1979 classic Alien was sometimes depicted by a man in a suit. Here's test footage of 6'10" Nigerian actor Bolaji Badejo practicing his extraterrestrial motions. Even with a mock-up of the xenomorph's head alone — and Badejo running around in his underwear — these reels remain unsettling.
For his only film role, Badejo — who was discovered in a London pub by a casting agent — studied miming, consulted H.R. Giger one-on-one to discuss the creature's gait, and endured the sweltering latex suit, which he could only safely wear for 15-20 minutes at a time. You can see a picture of Badejo sans helmet below.
Badejo appeared in shots where the creature's body was fully exposed. The suit's banana-shaped head didn't afford the actor a great deal of comfort or visibility, particularly when he donned the articulated special-effects helmet. As he explained to Cinefantastique magazine in 1979:
[The special-effects helmet] was all manual, remote controlled [...] There's still a space in it for my head. I had it on just to make sure nothing goes wrong with the posture of the head or how tall it is in comparison to the other sequences. They must have had about 2000 tubes of K-Y Jelly [...] just to get the effect of that slime coming out of his mouth. A lot of it was spread around on the face. I could barely see what was going on around me, except when I was in a stationary position, while they were filming. Then there were a few holes I could look through.