Expect huge amounts of derp and rage, punctuated by /tg/ extracting humor from it.
Commissar Dan is a commissar named Dan (hurr, though his full name is apparently Daniel Sterne). He has a pet basilisk (Fluffy), and uses it as a frontline tank. Is apparently with the Angry Marines for no other reason than he started tagging along and eventually people just got fed up asking why.
Not to be confused with Commissar Fuklaw, who is
similarly as awesome as Dan so much cooler than Dan nothing like as cool as Dan.
It is also thought that Dan is in fact an undercover cultist planning to destroy the Angry Marines by killing all the scouts. This will no doubt fail.
Turns out the crazy son of a bitch has joined Grendel, Boone and LIIVI in ascended to canon status, on page 116 of the Enemies of the Imperium supplement for Only War. Turns out he was ordering those pig fuckers to ram a Hellbrute! It went exactly badly as you can imagine.