Dijkstra has made many contributions to
computer science, primarily in the 60s when he was at
TU Eindhoven.
He developed a multitasking OS, worked on programming methodology and more specifically, structured programming.
He is well known for the letter to CACM exemplifiying these ideas, for Dijkstra's algorithm to operate on problems that can be described as graph traversals, and for semaphores.
For the production of text, Dijkstra preferred the use of handwriting to computers. Get the Dijkstra font if you want to know what it looks like.