Parasite

Parasites are a demonic possibly non-sapient creature from Hell. Very little information is given, or known about them.

Several parasites can be seen in tubes in Lazarus Labs, whilst their larger brethren parasites, control the Hell Guards and Hell Razer

Behind the scenes
The Parasite does not have an official name, and is instead given a generic title.

They partially resemble the Leech from the Half-Life series.