Который is the all-purpose 'which/who/that'

'The book that I read', 'the friend who came' — combining sentences.

Russian uses one word, который, where English uses 'which', 'who', 'that', and even 'whose'. The trick: который declines to match its noun in gender and number — and takes whatever case its role inside the relative clause requires.

Gender and number agreement

который agrees with the noun it refers back to: - Masculine: который. Друг, который пришёл = the friend who came. - Feminine: которая. Книга, которая мне нравится = the book that I like. - Neuter: которое. Окно, которое разбили = the window that was broken. - Plural: которые. Студенты, которые учатся = the students who study.

Case follows the role inside the clause

Который's CASE depends on what it does inside the subordinate clause — not on its role in the main clause. - Книга, которую я читаю = the book that I read. (которая → которую in accusative — direct object inside the clause.) - Друг, с которым я говорю = the friend with whom I'm talking. (which is masculine; instrumental because с governs it.) - Учитель, у которого книга = the teacher who has the book. (genitive after у.)

Comma rules

Russian always puts a comma before который. Это книга, которую я люблю. (Note the comma.) If the relative clause is in the middle of the main clause, there's a comma at both ends: Книга, которую я люблю, на столе.

Whose = чей or 'у которого'

For possession, the easy way is у которого (literally 'at which-one'): Друг, у которого новая книга = the friend who has a new book. In higher register Russian uses чей, but у которого is everyday.

Examples

Это книга, которую я читал.

This is the book I was reading.

Feminine accusative — direct object.

Друг, который пришёл, — мой брат.

The friend who came is my brother.

Masculine nominative — subject of the clause.

Студенты, которые учат русский, очень умные.

The students who are learning Russian are very smart.

Plural nominative.

Анна, с которой я говорил, — учительница.

Anna, with whom I was talking, is a teacher.

Feminine instrumental.

Учитель, у которого мы учимся, — старый друг папы.

The teacher whose class we're in is dad's old friend.

Masculine genitive after у.