He was the co-executive producer of the TV series Buffy the Vampire Slayer and co-creator of its spinoff, Angel.
He left the show at the end of the third season to co-create the spin-off series Angel with Joss Whedon.
On June 1, 2007, The Hollywood Reporter announced that he would serve as executive producer and showrunner on Moonlight, a similarly themed vampire detective show.
[2] He later had to leave the show prior to its debut for health reasons, but executive producer Joel Silver stated that his imprint would remain: "He worked really hard on the arc of the series.
"[3] Greenwalt is the co-creator and executive producer alongside fellow ex-Angel writer Jim Kouf.