A pronoun is a word that substitutes a noun or a noun phrase.
он - he
она - she
они - they
его - his
её - her
их - theirs
In the Russian language, pronouns can be divided into several categories:
Personal Pronouns
I (я), you (ты), he (он), she (она), it (оно), we (мы), you (вы), they (они)
Possessive Pronouns
my or mine (мой), your or yours (твой), his (его), her or hers (её), our or ours (наш), your or yours (ваш), their or theirs (их) 4
The Reflexive Pronoun
себя - this pronoun can mean myself, himself, herself, ourselves, themselves, etc.
Demonstrative Pronouns
this (этот), that (тот)
Interrogative Pronouns
who (кто, который), what (что), which (какой, который), whose (чей)
Indefinite Pronouns
someone (кто-то), something (что-то), anyone (кто-нибудь), anything (что-нибудь)
Negative Pronouns
nobody (никто), nothing (ничто), nobody to (некого), nothing to (нечего), no (никакой, никакая, никакое, никакие), nobody's (ничей, ничья, ничьё, ничьи)
Let's have a look at them, their uses and their endings in more detail: