Cybermen

look has stayed consistant.  
 
All Cybermen are seemingly just tall, humanoid robots. They all have high strength protective metal armour, sometimes plated onto integral parts of the body, with weaknesses in between, and sometimes covering the entire body in a thin, tin-foil like texture. On almost every Cyberman is a chestpiece. The chestpiece holds various equipment and gadgets, but most importantly, it contains their breahing apparatus. The very first Cybermen housed their weapons on their chestpiece. The most noticeable difference between the Cybermen and any other robot is their head. The crafted facial features,  including the trademark, tear duct eyes and straight horizontal mouth are a reminder of their completely emotionless state, though the most iconic feature are the handle bars on either side of the head. The purpose of the handlebars is apparently to "increase the speed of their brainfunction", though not all Cybermen have them. The Cybercontroller from the original series of Doctor Who had no handle bars, instead it had an enlarged, and partly transparent head, that displayed its brain.