I came across the word 变形金刚 in a short children's story that I read and Pleco dictionary states that it refers to either shape-shifting warriors protecting the Buddha, or Transformers (which Google displays almost exclusively if you search the term). Obviously the connection between the 2 meanings is clear.
But I'm unsure what is the meaning of 刚 in this phrase. I asked my wife but she even believed the character is 钢 so didn't have a suitable answer.
Is there a historic meaning of 刚, or a historical transformation (!) from another character to this current one, which would enlighten me as to why this character is used in this phrase?