Sire can refer to several things:

• Sire is a term for the father (or genetic species providing sperm) of a creature, contrasting to the female term, dam.
  For example, the sire of a mule would be a donkey, and the dam of a mule would be a horse.
• Sire is used as a form of address and title for a man of rank or authority, equivalent to Lord or Prince.
• Sire Records is a record label.
• In vampire mythology and fiction, a vampire's sire is the vampire that turned him or her into a vampire (which is now his or her childe).

In the case of the fictional Buffyverse see here.

Grandsire is the term for the sire of a sire, much like grandfather or grandmother.

• According to the Department of Canadian Heritage, the title of sire is given in conversation with a male monarch (king or emperor). http://www.canadianheritage.gc.ca/progs/cpsc-ccsp/pe/address4_e.cfm