The Slitheen are a fictional family of massive, bipedal extraterrestrials.  They are of the egg-laying calcium-based Raxacoricofallapatorian race native to Raxacoricofallapatorius. They are instinctive, ruthless hunters with a death sentence hanging over them on their home world. They first appear in 2005 and their last appearance was 2010 and they also appear in 'The Sarah Jane Adventures'.