I would absolutely go with Friedrich Nietzsche, not so much on the basis of "God is dead," as the last 40 years have been characterized by a revival of religious faith and religious conflict, especially in the Middle East, but because of his impact on how we understand language.
While Enlightenment philosophers saw language as a clear window pane revealing truth: they thought that to get the precise words down meant to have captured truth itself, Nietzsche turned that concept on his head. Language he said is not a clear window pane but a prison. We are caught, he famously wrote, in a "prisonhouse of language." What he meant by this is that while we need language to think, the language we learn is already tainted by the misconceptions and prejudices of past generations. As young children learning the language, we internalize all its limitations and errors before we are able to evaluate them. We are imprisoned by language that itself limits and distorts our ability to think clearly. In modern times, as we have moved away from the idea that intellectual authority lies in the hands of white European males, this concept has been used by post-colonial and feminist thinkers to show the ways prejudice against darker skinned people as "the other" is ingrained into the language. For example, in Harriet Beecher Stowe's Uncle Tom's Cabin, she makes a heartfelt and impassioned plea for the dignity of the slaves and for freeing them, but does so in the only language she knows, which is cringeworthy in its racism, referring, for example, to the blacks as childlike people who love to sing and dance.
Nietzsche also understood language not as the expression of truth, but as narrative. It is a story we tell that may or may not be correct and that is always influenced by power: the people who have the power tell a story favorable to themselves.
This radical questioning of language has had a profound impact on 20th and 21st century thinkers, including post-structuralists such as Derrida (who lived into the 21st century) and Foucault, who have had such an influence on contemporary thought in pointing out that thinking is based on sign (language) structures that are imperfect and thus open to deconstruction, as well as profoundly influenced by power.