Who is Shams from The Essential Rumi and what is their importance?

Shams was Rumi's first Friend. Just as the reader gets the impression that Rumi had difficulty finding a "kindred spirit", Shams appears. They became close friends, a friendship that made Rumi very happy, as their time together primarily included a lot of interaction and conversation.

One day, Shams went away, but he was searched for and returned. Finally, he simply disappeared..... never to be seen again and presumed murdered. It was after Shams' disappearance that Rumi began writing poetry, and Shams is seen as his inspiration.