Double Bass, Instrument or Part of Drums?

After the last interview I did, it got me thinking about Double Bass as an instrument or is it a part of drumming?

Kyle, from the Devour the Masses said he uses it in correlation to drums. I feel that it is to be considered a different instrument. It changes your style, it makes for a different feel, and depending on the use can really enhance the sound of your drumming. So yes it is a tool, but I would actually consider it an instrument within an instrument. Listening to a single bassist and a double bassist should allow for your own opinion. What do you think?