Dan Streetmentioner, also known as Dr. Dan Streetmentioner, was a grammarian and the author of Time Traveler's Handbook of 1001 Tense Formations, a manual on the grammar of time travel. His very lengthy and complicated work was of little practical interest to most readers, and later editions saved on costs by only in fact printing the first section of the book up to the Future Semiconditionally Modified Subinverted Subjunctive Intentional.