The halo effect is a cognitive bias where one's general assessment of another person or thing is influenced (positively or negatively) by one strong characteristic or trait. For instance, if we perceive a person as being good at A (A being a trait we approve of), we are likely to assume that they are also good at B, C, and D.
The halo effect was first coined in the 1920's by psychologist Edward Thorndike. He conducted a study where he had two military commanding officers evaluate various qualities of their soldiers categorized within four general groups: 1) Physical Qualities, 2) Intellect, 3) Leadership Skills, 4) Personal Qualities. The results were that the officers generally rated a soldier as either good in all four areas or bad in all four areas. Few were rated highly in one area and low in another.
Many later researchers have conducted studies which have supported Thorndike's findings. One study demonstrates the power that one particular characteristic can have on our thinking; that of beauty. The study was conducted in 1972 by Dion, Berscheid & Walster at the University of Minnesota. They showed 60 subjects pictures of three different people (an attractive, an average and an unattractive person) and asked them to rate the individuals in the photos in several different areas including personality traits, overall happiness and career success. The results were that those with attractive faces were judged to be superior in all areas compared to those seen as unattractive or of average looks. It was concluded that the ratings were the result of the 'What is Beautiful is Good' stereotype, which is essentially a type of halo effect. (1)