If it is a nile, and is aggressive and you want a tame monitor then it is probly not for you.
If your really looking for a calm tolerant easily handled monitor then first look at the species known to be docile. Then look for the docile species you like the most, then look for a docile individual. This is of course the easy method.
You could look for the one individual of any given species that fits the bill, but it may take awhile.
Now realize one could probly take any given monitor and have a chance at calming it down. But as I see it if you have to ask then your probly not ready to go about it.