Used in the Holy Quran in several paces to describe the duties of a prophet. People named Mubashir tend to be optimistic and trusting because of there undying faith in goodness of human. They are also easily taken advantage of because they believe that if they are good to everybody all the time then everyone will be good to them. They tend to have inclinations toward science and medicine. Now the funny thing is even though they are practically incapable of complain when someone treat them unfairly they will unleash hell if you treat their friend or anybody around them unfairly.
And surely our messenger came to Abraham with glad tidings.