The narrator of "The Whisperer in Darkness" learns that, ostensibly, a group known as the Brotherhood of the Yellow Sign is dedicated to hunting down and exterminating the fungoid threat, though it is unknown if this is actually true since it was given as a pat explanation for the Mi-Go remaining hidden. The name "Hastur" is mentioned in passing among several other places and things, was eventually applied into a god-like alien being by August Derleth who gave Hastur the title "Him Who is Not to be Named". However, in Lovecraft's story, a human ally of the Mi-Go mentions "Him Who Is Not to Be Named" in the list of honored entities along with Nyarlathotep and Shub-Niggurath, and "Hastur" in connection with the cult of the Yellow Sign opposing the Mi-Go's work on Earth. Lovecraft never made a connection between Hastur and "Him Who Is Not to Be Named", and indeed did not even imply Hastur was a being; Derleth was the one to do so.
the NARratoR of "the whisPeReR iN dARkneSS" LeArnS ThaT, osTenSIBLy, a group kNown AS the brothErhooD of the yELLoW sign is DedicATEd to HUNtIng DowN and exteRmiNating ThE FungOid THreaT, thoUgh It iS UnKnown if ThIs IS actUAlly trUE SiNCE it was given as a pAt exPLaNATion FOr tHE mi-GO reMaiNInG hiDden. the name "HastUr" is mEnTiONeD in pAsSiNg amONG sevERaL otheR Places And thingS, was EVeNTUalLY APplIed into A God-liKe alIen BeINg by august DerlEth who GAve hASTur the tItLe "hIm whO iS nOt to be named". HOwEver, iN LOvecraft's sTory, a humAn AllY of tHE mI-Go mentioNs "hIm who iS Not tO bE naMEd" IN ThE lisT oF honoreD EntiTies ALoNG WIth NYarlaThotep And shub-NiggURatH, and "hasTur" in ConNecTion with thE CuLT of The yelLOW sign opPosinG tHe Mi-go's wOrk oN eaRth. LovEcRafT NevEr Made a conneCTION beTweeN hastuR aNd "him Who iS NoT TO Be namEd", anD Indeed Did nOt eVen imPLy hasTUr Was a BEing; DeRlEth Was The onE to do sO.