One of Buffy’s sidekicks was nerdy guy named Xander Harris. Unlike the stereotypical nerd, Xander was not very smart. Even though he was pushing 30, he was still in high school. I think Ash mentioned that the man who played him was originally a sound-guy, but then he got the role as Xander.
I think the purpose of Xander’s character is so fanboys who watch the show have a character they can relate to in the cast. These nerds can vicariously live through Xander and pretend that they have a blonde friend with super-powers. Even though Xander is in love with Buffy, like the fanboys in real life, he never got to date her.
Xander’s love-life was pretty unusual. He was only attracted to women with supernatural powers or demons. He was first in love with Buffy, who had demon-powers. He also fell in love with a praying mantis monster, a witch, a woman who later got demon-powers, and he almost married a former demon.