Who is Shiva from The Bhagavad Gita and what is their importance?

Shiva is the Destroyer of the Universe. In the book Krishna refers to Shiva solely as Time. However, he refers to Shiva in direct relation to the fact that they are facing the need to kill adults today upon the battlefield. Krishna urges Arjuna to not even think of himself as doing it, but to see that Time is the Destroyer and that everyone is going to die at some point regardless of their behavior today.