His character was shown by his treatment of Zeeta.

The poor child slaved all day and did two men's work in keeping the household going.

She was an orphan from a mission station, and in Japp's opinion a creature without rights.
Hence he never spoke to her except with a curse, and used to cuff her thin shoulders till my blood boiled.

One day things became too much for my temper.

Zeeta had spilled half a glass of Japp's whisky while tidying up the room.