There are a couple of band/artists with the name 'Sullen':

1) St. Louis based rock/punk outfit fronted by Justin Slazinik and Shanna Kiel.
Both share guitar and vocal duties, while Justin's guitar is set up to play both the bass and guitar parts similar to Local H's setup.
In 2003 they released Paint the Moon on Chicago's premier punk label, Thick Records.
They toured extensively with bands such as Local H, Verbena and Jucifer.
However, inner-turmoil caused the band's demise and each founding member has their own respective bands.
Shanna fronts Black Fur
Justin Fronts The Axis Club

2) A Scottish acoustic artist (real name, Gary Rankin) who is based in Glasgow.

3) American crossover/rap core band. They released the album "Sapients" in 1995.

4) Portuguese progressive metal band. They released the albim "Post Human" in 2015. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.