Journalist Walter Lippmann popularized the word in his 1922 book Public Opinion. A stereotype was originally a metal printing plate that reproduced the same image over and over. Lippmann used it to describe the fixed "pictures in our heads" people use to make sense of others.
In the US, racial stereotypes were often created to justify how a group was treated. Caricatures of Black people as lazy or dangerous were used to defend slavery and later Jim Crow. Native Americans were cast as savage to justify taking land. Asian Americans have been portrayed both as a threat and as a model minority, a stereotype used to dismiss other groups' claims of discrimination.
Stereotypes have measurable effects. They feed implicit bias in hiring, medical care and school discipline. They can also affect the people they target: research on stereotype threat shows that reminding someone of a negative stereotype about their group can lower test performance. Media portrayals matter because they are many people's main exposure to groups they rarely meet.