The relative pronouns

Relative pronouns introduce relative clauses.

The following are relative pronouns:

Pronouns der, die, das are more frequently used than the other relative pronouns.

Pronouns welcher / welche / welches have the same function but are rarely used because they are considered stylistically inferior.

 
In addition pronouns wer and was are basically interrogative pronouns that, in some cases, function as relative pronouns.