Wolfgang Köhler

Wolfgang Kohler (21 January 1887 - 11 June 1967) was a German psychologist who, like Max Wertheimer and Kurt Koffka, helped create Gestalt psychology. He was the first to show that apes could solve problems by thinking.
Gestalt psychology
In 1910-13, he worked with fellow psychologists Max Wertheimer and Kurt Koffka. He and Koffka were subjects for Wertheimer's studies, which led them to conclusions about the nature of vision. They collaborated on the founding of a new holistic attitude toward psychology called Gestalt theory, from the German word for "whole". This was influenced by some earlier work of Carl Stumpf (Kohler's teacher) and Christian von Ehrenfels. Wertheimer had attended Ehrenfels' lectures at the University of Prague.
Kohler's famous quote, "the whole is different from the sum of its parts" is usually quoted differently. Though perhaps a simple error made in translation, many lectures in textbooks of modern-day psychology quote Gestalt theory by saying "the whole is greater than the sum of its parts". It is difficult to imagine that a translation error occurred here, especially when considering that 'greater' is 'grosser' and 'different' is 'unterschiedlich' in German, respectively.
Problem solving
In 1913, Kohler left Frankfurt for the island of Tenerife in the Canary Islands, to be the Director of the Prussian Academy of Sciences anthropoid research station. Here, Kohler observed how chimpanzees solved problems, such as that of retrieving bananas when placed out of their reach. They stacked wooden crates to use as makeshift ladders, in order to get the food. If the bananas were placed on the ground outside the cage, they used sticks to lengthen the reach of their arms.
Kohler concluded that the chimps had not arrived at these methods through trial-and-error. American psychologist Edward Thorndike claimed this was the basis of all animal learning: his law of effect. Instead, the chimps had an insight (also known as an "aha experience"). They saw the answer mentally, then they got the bananas in a way which was, in Kohler's words, "unwaveringly purposeful".
So, he concluded that the animals were capable of problem-solving and that they did not arrive at their methods through trial and error. This is one of the most important findings from the research done on apes. Kohler's work on the mentality of apes was a turning point in the psychology of thinking. In the book The mentality of apes, Kohler explains that he was inspired to work with the chimpanzees for two main reasons. The first was because the "structure of their brains is more closely related to the chemistry of the human body and brain-structure than to the chemical nature of the lower apes and their brain development" Kohler (1925). The fact that human traits can be observed in the everyday behaviours of this animal was very intriguing for Kohler. Kohler also wanted to gain knowledge of the nature of intelligent acts.
Kohler recognized that, like humans, there is a great deal of individual differences in intellect. Chimps showed that they were able to grasp the objects around them in a variety of fashions. This is incorporated in their everyday playing behaviours. For this reason, it was not necessary to use experimental tests to introduce chimps to handle matter. In his book, Kohler describes how the apes use their hands: "large, powerful and flexible hands are natural links between himself and the world of things, and he attains the necessary amount of muscular force and co-ordination at an earlier age than the human child" Kohler (1925).