Deism is a belief that God created the Universe, the earth and everything else, but then went away and took no further interest in his project or in human affairs. A deist believes in deism, in practise deists tend to think and act like atheists.
A large number of deists believe that the "Big Bang" was somehow initiated by God and everything that happened since is the consequence of scientific laws which were "created" at the same time. There is no evidence for the existence of such a being.
In fact, the first deists were the atheists of their day. They clearly saw that God obviously did did not (indeed could not) exist in the form that many people believed. That is to say there is evidently no being interfering in our lives on a daily basis, answering prayers, guiding evolution or whatever.
Consequently, being unable to drop the idea of god completely, they came up with the idea that he had simply kicked the whole thing off and then gone "somewhere".
Deists believe in a god rather than a pantheon of gods. There is no rational reason to prefer a single god to a pantheon of gods but deists grew up and lived/live in a monotheist culture and were/are influenced by their culture.