So according to this page I found one day, there's an alleged cheat that says you can bomb an entire park to get $10,000,000 as it said here:

Find guest 2374 and rename him Timothy McVeigh. Then, make him walk pass an entertainer. Next find a slide, look for a big bomb to go down it. Afterwards, all guests, rides, etc. will be gone and you will have $10,000,000.

There's also two other cheats that make strange allegations too. In addition to that, there's a few cheats where you name guests such as "BigBucks", which is a cheat that would give you infinite money, which didn't work for me. There's also the name "John Bubrough" cheat where pressing the 'L' key makes stuff happen, which also didn't work for me.
These cheats can also be found on other webpages besides the one I linked here, but some of the name cheats on that page do work.
With that said, who made up those RCT1 cheat codes?

who made up those RCT1 cheat codes?

the devs

who made up those RCT1 cheat codes?

the devs

So the game developers actually were the ones to make up the cheat codes? Why would they want to do that?

the devs

So the game developers actually were the ones to make up the cheat codes? Why would they want to do that?

Any number of reasons. From pop culture references (i.e. Mr. Bean) to touchy references like this one. Only the devs know why they made the cheats and named them the way they did.

Some cheats are only active if you use a "trainer" which basically modifies the game. I used to use one so I could basically do Sandbox mode back on my XP. Some features included pressing Shift + 4 to add money, pressing alt + ctrl to send a tram-full of guests into the park, and so on.

There's no way of knowing who made up these cheats if there's no proof that they actually work. For the Timothy McVeigh cheat, many people have blindly copied it from other cheat websites along with working RCT1 cheats without testing it out first--some websites have a note where the poster specifies that they haven't tried any of the cheats. So far, nobody anywhere has confirmed that this cheat actually does anything.