Life sure seems like a series of pronoun referent errors sometimes. Am I, as Descartes would suppose? Or is Sartre to be believed, and is what seems to be I really a He? Perhaps I am really a we, a near infinity of selves, overlapping at points to create the illusion of existence. It gets even more dizzying when grammatical case is applied. Am I or is Me? Subject or Object?
Grass here throws the entire question into the blender by slapping the genitive case on the title, and then doggedly refusing to clarify. One would assume that the century in question belongs to the author, and for large stretches of the book that is true. He, or some version of him, is the I of many of the chapters, and there is an air of straightforwardness to those years that leads the reader to trust their account.
More often, however, "I" is as far removed from Grass himself as possible. Presumably fictional characters, historical figures, and often narrators without any perceptible identity at all. The book culminates in a Gordian knot of identity, where I is not only a real person--the author's mother--but also quite explicitly dead while narrating.
While Grass leaves us in this pronominal quandary, however, he at least does so knowingly. "I'm He now," says the narrator in "1972". "He--no longer I--never had an easy time of it" (191). The I, the narrator of the story, is in this section explicitly as fluid as the narrator of the whole book is implicitly. The genitive, eponymous owner of the century is both I and They and, to the extent possible, You. It is only in this way that Grass can capture the most turbulent 100 years that humans had known up until that time in ". . . rhymed and unrhymed poems and short stories and overly long chapters representing 1) work currently in progress on both sides of the wall, and 2) the world in miniature" ("1975", 202).