Who is Silas from The Graveyard Book and what is their importance?

Silas is one of the undead, possibly a vampire, who is allowed Freedom of the Cemetery. When the baby first arrives at the cemetery, Silas uses his powers to distract humans. He later agrees to be the child's guardian. Over time, Silas becomes a father figure, providing answers for his many questions. Silas later makes the big decisions for Bod, deciding if he should attend school and deciding when it is time for Bod to go out into the living world on his own. Silas cares deeply for Bod and places his own life on the line to keep him safe from the Jacks of All Trades.