Rudolf Lingens

Rudolph Lingens is a fictional character often used by contemporary analytic philosophers as a placeholder name in a hypothetical scenario which illustrates some feature of the indexicality of natural language. He was created by the logician Gottlob Frege in the course of one of the earliest systematic discussions of indexicals. A number of philosophers picking up on Frege's discussion of indexicals, notably John Perry, David Lewis, and Robert Stalnaker, have adopted Lingens to make their own points about indexicals.
"De se" attitudes.
Lingens first appeared in Frege's influential essay 'Thought' ('Der Gedanke', published in "Beiträge zur Philosophie des deutschen Idealismus I" (1918–19), pp. 58–77). Mr. Lingens appears in the company of Leo Peter. Both are concerned with Dr. Gustav Lauben's having been wounded, and are later joined by Herbert Garner who is possessed of the knowledge that Gustav Lauben was born on 13 September 1875. Frege's discussion is concerned with how proper names and indexicals like 'I' function and how they are connected with the sense (or mode of presentation) that, on his account, each speaker who uses them associates with them.
Rudolph Lingens makes a number of appearances in the subsequent literature on Frege and on indexicals. Notably he occurs in an influential 1977 paper by John Perry ('Frege on Demonstratives'), in which Perry asks us to imagine Lingens as an amnesiac in Main Library at Stanford who comes to read a complete biography of himself. By reading the biography, Lingens comes to have a rich body of factual information about Rudolph Lingens, but he still fails to realize that (as we would put it) "he himself" is Lingens. Here we resort to natural language indexicals—"he himself"—to try to express what knowledge it is Lingens lacks; and our resort to such indexicals for expressing this knowledge seems to be ineliminable. Much of the philosophical literature on indexicality is concerned with trying to explicate the apparently "essentially indexical" character of the information Lingens lacks in Perry's imagined scenario.
Attitudes that essentially require indexical reference to oneself to express—such as the belief Lingens would express by saying "'I" am Rudolph Lingens'—are often called "de se" attitudes.
Lingens reappears in David Lewis's 1979 paper on the topic ('Attitudes "de dicto" and "de se"') and also in a 1981 paper by Robert Stalnaker ('Indexical Belief'). Both philosophers are picking up on Perry's discussion. 
In this paper, Stalnaker suggests that Lingens is the cousin of Bernard J. Ortcutt, a character originally created by W. V. O. Quine to illustrate the distinction between "de dicto" and "de re" attitude ascriptions.