The "well-planned name of Missingno" (and even the number 000) in Red and Blue comes from the programmers deliberately including Missingno in hopes that if anything were to go wrong, the game would only display this bizarre text as opposed to crashing. It was made in Ruby and Sapphire too, and cheating devices can be used to extract it from its legally unassailable location, or, as I'm A Potato said, you have extraordinarily slim odds of finding it. But of course it was not the programmers' intentions to have you actually FIND Missingno in the bizarre way it got included in Red and Blue. That was an accident. So why do you see Missingno? Prepare for a long, possibly tedious or even soporific, explanation.
It works like this. The programmers wanted that old man to teach you how to work pokeballs, right? So when the old man gets in a fight with that Weedle, the programmers had to have the name "OLD MAN" in place of your name. In order to make that happen, the characters for your trainer's name had to be stored somewhere for later retrieval, so you wouldn't go through the rest of your pokemon journey with the name OLD MAN.
So what happened was they made the storage space where information of wild pokemon is normally located, figuring they'd be safe because you can't run into wild pokemon in Viridian City. When the OLD MAN's fight with Weedle would end, the name would be retrieved and when you were to go into another area, the storage space for your name would be replaced with actual data of the wild pokemon that appear in that particular area.
However, the glitch is that when you fly to another
city, the wild pokemon data does
not get replaced, since cities don't have any wild pokemon. On Cinnabar Island's coast there is no wild pokemon data; this is where the glitch came from. If you were to have come directly there from surfing around, you'd find whatever pokemon you encountered while surfing around. If you were to come directly from the Safari Zone, you'd see Safari Zone pokemon. Come there from any particular location and you'll find whatever particular pokemon are normally found on that location (and you'll have the exact same odds of finding any single pokemon)
But since the "wild pokemon" of Viridian City is actually the characters of your name, the game mistakes the data of your name for pokemon encounter data. Three characters of your name are associated with pokemon and three are associated with that pokemon's level. By manipulating your name, you can make almost any encounter you wish.
So how do you get Missingno? Well, the three characters in your name are used to determine your place on a table that goes from 0 to 255 (don't ask me how, I'm not sure how it works). But I do know that there are only 151 different kinds of pokemon. The other 105 slots? They're what get you your Missingno.
Missingno was indeed designed by the programmers, and it was meant never to be seen unless the game totally malfunctioned. Cinnabar's coast not having wild pokemon data and your name being replaced with "OLD MAN" were what unintentionally exposed it. Ruby and Sapphire possess Missingno as well, but, as Ruby and Sapphire don't have such a glitch, only cheating devices can reveal it unless you're extremely fortunate. I hope I correctly answered any queries on the mysterious Missingno
