He was also President of the Queensland Branch of the Clydesdale Horse Society and a Freemason.

[1] On 12 January 1910 Muller married Annie Lobegeiger (died 1970)[2] and together had one son and three daughters.

Muller was accorded a state funeral upon his death[1] and during the condolence motion in Parliament, his son Selwyn said the advice his father gave him upon winning Fassifern was "Use your common sense.

If you have anything worthwhile to say, have the courage to say it; if you wish to comment but are not aware of the facts, remain silent".

It was stated at the time that these differences related to transactions Muller had with the Income Tax Department.