The Country of Rus, Tartary, Muscovy are all names once used for roughly what we now call Russia.
Russian can be used as both a noun (referring to a person from Russia) and an adjective (describing something related to Russia). So, it can take on different grammatical roles based on how it is used in a sentence.
Gibraltarian is the demonym of Gibraltar.
The name for the people - demonym - of Albania is Albanian.
The name for the people - demonym - of Afghanistan is Afghan.
The demonym for Hemel Hempstead is "Hempsteadian."
The demonym may be Geelongian or Geelongite.
A person who lives in Laval is called a Lavalois if they are male and a Lavalloise if they are female.
Cuban
Belgian
Singaporean
Belgian
Vancouverite...