Answer:
Richard Lazarus
You probably picture most psychologists as being calm and rational individuals, right? Well, not exactly. In fact, in the 1960s, there was a heated war going on between two camps of psychology: the behaviorists and the cognitive psychologists.
Behavioral psychology approached emotions and thoughts as window dressing and maintained the belief that the major driving force within people is their responses to rewards and punishments from the world around them. For example, if you give someone a chocolate cookie every time they go running, they'll want to go running more because they will associate it with the reward of chocolate chip cookies. Never mind that they won't lose weight that way!
On the other hand, cognitive psychology focused on the importance of thoughts and emotions in the way that a person lives from day to day. For example, if someone is trying to lose weight, cognitive psychologists believe he needs to change the way he thinks about food and exercise, learning to appreciate healthy foods and learning to think positively about exercising.
In the middle of the 20th century, behaviorists ruled the field of psychology. Thoughts? Feelings? Most psychologists didn't put much stock in those!
But Richard Lazarus stood up for thoughts and feelings. He studied people's stress levels and said that events are not good or bad, but the way we think about them is positive or negative, and therefore has an impact on our stress levels. For example, say that you are late to work and the person in line in front of you at the coffee shop is taking forever to order what he wants.
The fact that the person is taking that long isn't good or bad by itself. But you believe that it's a negative experience because it's going to make you late to work, which makes you feel stressed out.
On the other hand, you could look at that situation and say to yourself, 'So what if I'm late? This is actually good because it's giving me a few extra minutes this morning to catch my breath before going into the office.' You think of it as a positive experience, and therefore you don't feel stressed out.
Lazarus's theory is called the appraisal theory of stress, or the transactional theory of stress. You can remember this because the way a person appraises the situation affects how they feel about it. According to this theory, there are two things that a person thinks when they are faced with a situation. These are called the primary appraisal and the secondary appraisal.