If you haven't watched the season finale of Galactica, don't read this. But if you have, it's time for a definitive revelation: Luke's father was really a Cylon.
During the episode in which the humans and the Cylons discover the wasted Earth, they come across the remains of its civilization. One of the things they found was a "2000-year-old, ancient Cylon." That was the phrase in the script, which was used by VFX supervisor Gary Hutzel and chief model maker Pierre Drolet to create the Cylon you see above.
Like Ralph McQuarrie did for Darth Vader, the pair took inspiration on classic samurai armour designs. The result was what you can see above, which clearly came way too close to the Dark Lord's helmet. So close that they took a couple of layers out of the helmet, to make it look like the skull on the right, which is the model that finally ended up in the actual shot:
Beautiful design either way, although I liked the full helmet better. I don't care it looked like Vader's, specially when McQuarrie also did art for Battlestar Galactica (some of it is under these lines.) [Darth Mojo—Thanks Alice]