Hermann Ebbinghaus

Hermann Ebbinghaus (24 January 1850 – 26 February 1909) was a German psychologist. Today, he is mostly known for his work regarding learning and forgetting. He was the first to do experiments to explore how memory works. He first described the forgetting curve, the learning curve and the spacing effect. The Ebbinghaus illusion, which is named after him is related to the perception, not memory. His son was the philosopher Julius Ebbinghaus. 
In 1896, he did a test on children in school: The pupils had to complete sentences, and their teacher had to rate each pupil, if the pupil was in the lowest, the middle or the highest third of all the people in the class. Ebbinghaus saw a relationship between the teacher's rating, and the result of the pupil, but he could not give a correlation (because he was lacking the tools to do so). This was possibly the first test of verbal intelligence in a group. 
Many of his experimental methods to rate memory performance are still in use.
Ebbinghaus died of pneumonia, when he was 59 years old.