From Battlestar Wiki, the free, open content Battlestar
Galactica encyclopedia and episode guide The Cylon Centurion is
a fully armored, metallic automaton that functions as the basic
foot-soldier of the Cylon ground forces. Modern Centurions serve
a variety of functions within the Cylon hierarchy, acting as
guards, soldiers, executioners and even gardeners. "Bullethead",
"clanker" and "chrome job" are common Colonial nicknames for
these advanced and deadly Cylon constructs ("Downloaded",
"Rapture", Battlestar Galactica: The Resistance). They are also
referred to as "toasters" - the common Colonial nickname (or
epithet) for the Cylon race as a whole (Miniseries,
"Resistance"). Although Centurions are sentient by design, an
implant annuls their higher cognitive functions and prevents
them from exercising full self-awareness ("Six of One"). It also
appears that this implant precludes them from harming any of the
humanoid Cylons, except by explicit order ("Hero"). According to
Sharon Agathon, this was done to pr