Sire can refer to several things:

It 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.

In vampire mythology and fiction, a vampire's sire is the vampire that turned him or her into a vampire.

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