Joss Whedon is the creator of several popular television series, namely Buffy the Vampire Slayer, Angel, Firefly, and Dollhouse, and the webseries Dr. Horrible's Sing-Along Blog. His collective work is referred to as the Jossverse, and his shows all have a large presence in fandom.
Mr. Whedon's penchant for explaining events and themes in the canon via press conference or news articles has seen him become the namesake of the trope, "the Joss"—essentially, the creator explaining something outside of continuity (and killing a whole bunch of fan theories in the process).
Mr. Whedon is also well-known for not being afraid to kill off beloved main characters in the course of a show, often at or near the climax. Since this sort of behavior is unusual for most writers, even the most genre-savvy fans may find it difficult to predict these twists, even knowing to expect them. This means two things: one, Mr. Whedon's name is routinely cursed by people just coming to said twists for the first time; and two, it's such an awesome ride that we can't wait to come back for more. Y'know, once we stop crying.