Stereotypes

What is a stereotype?
A stereotype is the instant idea that we get about a person's personality just by the physical traits they have. We tend to group those with similar traits together and automatically think they have the same personality (eg. all blondes are dumb). We seem to judge those on their appearance and build up our thoughts of them on our initial views of them.

How and why do we stereotype?
We stereotype by making judgments on people by what they look like before we get to know them. We stereotype because it is harder to get to know somebody and understand what their personality is like than to use the existing ideas that we already have of people who look like that or have the same characteristics. People also stereotype because that's how our brains are programmed. No matter whether we think it is wrong, you'll always subconsciously do it. " "Mahzarin Banaji, psychology professor at Yale University explains, "Our ability to categorize and evaluate is an important part of human intelligence. Without it, we couldn't survive.""This is a very true statement. Even though stereotyping may be bad, without stereotyping, how would we know what is bad? If someone wearing all black and had only little slits for eye holes was coming after us, would we know that it's bad? So even though it is negative it does have positive purposes too.

Why do the media use stereotypes?
The media uses stereotypes so that it is easier for the audience to watch. It allows the audience to use their preconceived ideas/ existing ideas on the characters rather than making them figure it out for themselves. This means some actors can be seen playing similar roles due to the stereotyping.

An example of how stereotyping can be seen in the media in glee. When we first watch glee, we see... 
-Quinn: the popular, catty blonde who is the cheerleader everyone wants to be
-Brittany: the dumb blonde, who also is a cheerleader.
These two different stereotypes in glee show the two different stereotypes that are commonly used in media, the dumb blonde and the popular blonde. By using these stereotypes we automatically have an opinion on these girls and it is not until much further on in the show that we can see their personalities may not be entirely what we had expected. For example at the end of season 3 we see Quinn as the nice girl rather than the catty, mean one, which took 3 whole seasons to change our initial opinion of her personality that we had stereotyped from that first episode. 
https://www.smartlivingnetwork.com/psychology/b/why-we-stereotype/