Silent protector of the castle, around long after all others have left. Wielding either water or fire, nothing shall cross this defender.

The sixth out of seven, In Leviathan’s den, Forbidden by heaven, In the tenth out of ten. To Goethe, I’m yellow, To Shakespeare, I’m green, I see all that you have, And I want what I’ve seen.

I am an entire era of humanity. Two is my formula. When I am created, it is done with labour and likely followed by ancient calamity.

Like a choice between, Like a metal unrefined, I sound like both of these, But it's not how I'm defined. With 'B' a pig's my brother, When sails give out I'm good, In days of yore moved to the beat of a drum when I was made of wood.

I knew much honour. But no longer exists. I knight from the past. Yet in a serie I am called Jack. Now don’t fear my blade, and guess my aid. What am I?