“The dog, who was called Rover, went mad.”  Use which.

What, That

That is applied to persons, animals, and things.  What is applied to things.  The antecedent of what should not be expressed.  What is both antecedent and relative.

“All what he saw he described.”  Say, “What he saw,” or “All that he saw,” etc.

Uniform Relatives

When several relative clauses relate to the same antecedent, they should have the same relative pronoun.

“It was Joseph that was sold into Egypt, who became
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governor of the land, and which saved his father and brothers from famine.”  Change that and which to who.

Choice of Relatives

Since who and that are both applied to persons, and which and that are both applied to animals and things, it often becomes a serious question which relative we shall employ.  Much has been written upon the subject, but the critics still differ in theory and in practice.  The following is probably as simple a statement of the general rule as can be found: 

If the relative clause is of such a nature that it could be introduced by and he, and she, and it, and they, etc., the relative who (for persons) and which (for animals or things) should be used in preference to the relative that.

“Man that is born of a woman is of few days, and full of trouble.”  The language of the Bible and of Shakespeare must stand, although the forms of expression differ greatly from those employed at the present day.  According to modern standards, that should be who.

“The earth is enveloped by an ocean of air that is a compound of oxygen and nitrogen!” Change that to which.

The relative that should be used in preference to who or which: 
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(1) When the antecedent names both persons and things; (2) When it would prevent ambiguity; (3) After the words same, very, all; (4) After the interrogative pronoun who; (5) After adjectives expressing quality in the highest degree.

“The wisest men who ever lived made mistakes.”  Use that.  See (5).

“He lived near a stagnant pool which was a nuisance.”  Use that.  See (2).

“All who knew him loved him.”  Say that.  See (3).

“Who who saw him did not pity him.”  See (4).

“He spake of the men and things which he had seen.”  See (1).

“These are my pupils which I have brought to see you.”  Use whom, as which is not applied to persons.

“This is the window whose panes were broken by the rude boys.”  Use “the panes of which.”  Because of its convenience, perhaps, the faulty whose is very largely used; as, “The eagle whose wings,” “The house whose gables,” “The ocean whose waves,” “The vessel whose sails,” “The play whose chief merit,” “Music whose chief attraction,” etc.
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