'Mr' , 'Mr.' , 'mr' or 'mr.' ? What's the correct?

The honorific should always be capitalised. A period after the contraction of a title is usually used in the US, Canada and South Africa, while in Britain and most other Commonwealth countries a period is not used. Style guides may call for a specific form (period or no period) in particular types of academic writing. Otherwise, just pick a form and be consistent with it. :)

either of the capital "Mr" or "Mr." is correct, but lower case is not

Lisa's father is Mr Johnson, chairman of A&F Inc.

Mr , is the british version of writing,"Mr." ,is the american version of writing  ,both are correct ,but I personally prefer "Mr.".(mr doesn't work)

it is Mr because you are adess someone 

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