Niemand vs. keiner
In German, both niemand and keiner can translate to nobody or no one, but they are not always interchangeable. The core difference is that niemand refers exclusively to people, while keiner can refer to both people and things.
Niemand
A1The word niemand is an indefinite pronoun that means nobody or no one. It refers exclusively to people. It is the direct opposite of jemand (someone) and must be declined in the accusative and dative cases.
Niemand war zu Hause.
(Nobody was at home.)
Ich habe heute niemanden getroffen.
(I met no one today.)
Sie vertraut niemandem.
(She trusts no one.)
Niemand kennt die Antwort auf diese Frage.
(Nobody knows the answer to this question.)
Keiner
A2The word keiner and its variations are pronouns that can mean nobody, no one, or none. It can refer to people, objects, or animals. When referring to people, it often implies not a single one from a specific or previously mentioned group. It must be declined to match the gender and case of the noun it replaces.
Viele wurden eingeladen, aber keiner ist gekommen.
(Many were invited, but no one came.)
Ich suche meinen Mantel, aber ich finde keinen.
(I'm looking for my coat, but I can't find one.)
Ich wollte eine Brezel kaufen, aber es gab keine mehr.
(I wanted to buy a pretzel, but there were none left.)
Hast du ein Taschentuch für mich? Nein, ich habe keines.
(Do you have a tissue for me? No, I don't have one.)
Von meinen Freunden hat keiner Zeit.
(None of my friends have time.)
Summary
The fundamental difference is that niemand is used only for people, whereas keiner can be used for both people and things. When referring to people, they are often interchangeable. However, keiner typically implies not one from a specific group, while niemand is more general, meaning no person at all. A simple rule is: if you are referring to an object or animal, you must use a form of keiner. If you are making a general statement about the absence of any person, niemand is the most natural choice.