I was wondering a lot about it lately. I found various examples of it, specially in more formal/old texts.

The first time I realized it was reading what Oppenheiner said in an intreiew after the test with a nuclear bomb, he quotes the Bhagavad-gita and says:

"Now I am become death, the destroyer of worlds.

What is this am doing there? What is its function? I am not an english native speaker, so I found it very tricky to find out the logic behind it, maybe some older tense I'm not aware of, or maybe "become" is not funcioning like a verb in an older context (but I think it is not as likely, knowing abou germanic languages in general).