Sire is the term used to refer to a vampire after he or she has transformed a human into a new vampire.

The term is also used as a verb (To Sire) to refer to the act of transforming a human into a vampire. 

List of Sires

The Master: to Darla and Yuki Makimura

Darla: to Angelus and Sarah Holtz

Angelus/Angel: to Penn, Drusilla, Sam Lawson and Theresa Klusmeyer

Drusilla: to Spike, Sheila Martini and Darla

Spike: to Anne Pratt, Holden Webster, Charlotte, Billy Fordham and various others 

Willow Rosenberg: to Sandy

Harmony Kendall: to Brad Konig and Justin

Knox: presumably to Alonna Gunn

Unnamed vampire: to Charles Gunn (time reversed)

Icarus: to Harth Fray (Harth sired himself by biting Icarus) 

See Also

• The Master's bloodline

Behind the scenes

• There's no official term to refer to the vampire who has been sired. Fans sometimes employ the term Childe, which is used the the RPG Vampire: The Mascarade. Another popular term is Fledgling.
• In "School Hard," Spike refers to Angel as his sire. While Spike was sired by Drusilla, Joss Whedon has commented that the term "sire" can refer to any vampire in a lineage: thus, since Angel sired Drusilla, he can also be considered Spike's sire. By contrast, Spike refers to Angel somewhat more accurately as his grandsire in "Just Rewards."