There were several historical Diogeneses. You’re looking for Diogenes of Sinope, also known as Diogenes the Cynic. (Formerly a poster here too, but got banned a few years ago.)
ETA: You’ve probably seen the famous trope, an image or drawing of an ancient toga-clad Greek carrying a lantern. That Diogenes.
I do have to wonder whether the o.p. has ever been in a cattle yard or feedlot. This idea might seem desireable on an individual level from a totally naive standpoint but beocmes untenible even as a concept once you consider the, uh, downstream implications of sucha diet. (To be fair, there are ruminants that are not as utterly disgusting in terms of fecal output as cows and sheep, but they’re even less efficient at processing grass or most leaves into free glucose.) And at a basic metabolic level, we need more than glucose; there are essential vitamins we would have to be able to extract or synthesize, and of course the essential amino acids which humans cannot synthesize. While all of these can be provided by some combination of vegetable matter (in particular, certain legumes) they are not going to be provided by grasses and leaves in sufficient density.
It would literally be easier to make human beings able to be sustained on a diet of processed sewage than to digest cellulose as the primary metabolic fuel.
Well, if some bacteria was going to help humans eat cellulose to the point where we wouldn’t need specific complex carbohydrates in our diet (I’m assuming that’s the point- we’d still need fats, proteins and vitamins), that would help with world hunger, as far as few people would need to starve, since they could just go eat some old newspapers or something like that to sustain themselves.
The bigger implication is that we’d have a ready-made biofuel bacteria; any kind of bacteria able to let humans eat cellulose with our current digestive systems would pretty much be something that would be able to change cellulose to sugar really quickly and completely, and that would be immensely useful for fermenting cellulose into ethanol for motor fuel.
So while it might be good for people in extremis (who’s going to eat sawdust or an old cotton sheet by choice), it would be really helpful in getting the world away from petroleum.
This really isn’t that far-fetched as people in some nonindustrial societies have been found to have special intestinal flora that can ferment cellulose into short-chain fatty acids.
