Clark has made numerous Marvel cameo appearances
DC and Marvel Comics have been friendly rivals for a long time now. They've never had a Sega/Nintendo style relationship, where they took shots at each other in the media in any serious way. They have even collaborated on numerous occasions, with both universes crossing over in different ways.
Not every appearance needs to be highly publicised crossover, nor do they always need to be official. Sometimes a subtle cameo is all that is needed - a knowing wink to the audience about the so-called "distinguished competition". With Marvel not being afraid to include references to DC in their works, it should come as no surprise that Clark Kent has appeared over 22 times in Marvel comics.
With Clark Kent having such an iconic design, it is easy for a square-jawed journalist wearing glasses and a blue suit to show up at crime scenes without DC's lawyers getting involved. He has even been referred to as "Clark" or "Mr. Kent" on various occasions.
No One Recognizes Clark Due To Super-Hypnosis
So why is it that no one recognizes Clark Kent as being Superman?
There have been numerous answers to this question over the years. He has used robots that look like Superman/Clark Kent in order to throw off suspicion. He would vibrate his face using super-speed, so that it would appear blurry in photographs. The Christopher Reeves Superman movies even had him using a memory wiping kiss, in case someone discovered the truth.
For a time in the 1970s, the official explanation for why no could see through the disguise was due to "super-hypnosis". Clark Kent's glasses are actually made from a special Kryptonian glass (presumably from the shuttle that he came to Earth in), that constantly emit waves of hypnosis that trick people into thinking he looks different. This explanation has quite a few holes in it, however. What would happen if he ever took his glasses off/had them stolen? What about all of the times he has appeared on camera (he is a reporter after all) or in a photo?
He Is Named After Two Of The Most Famous Actors Of All Time
The story of the creation of Superman is one fraught with sadness and tragedy.
In 1932, the father of Jerry Siegal (one of Superman's creators) was murdered during a robbery in a clothes store. It is ironic that this crime would mirror the origins of Batman, even thought it ultimately led to the birth of Superman. As time went on, Jerry Siegal imagined a hero that bullets would not harm. Combining his writing talents with those of an artist friend named Joe Shuster, they created the character that would go on to be known as Superman. The two would not get their financial due, however, as they sold the rights for the character to National Comics for $130. They would spend the rest of their lives in court, trying to get a small piece of the icon that they created.
The character of Clark Kent is named after the two biggest actors of the day, Clark Gable and Kent Taylor. Clark Gable was referred to as the "King of Hollywood", and is one of the most consistent box-office draws in movie history. Kent Taylor is less well-known, but he had one of the most prolific careers in early Hollywood, starring in over 110 movies.
He Built Robots To Protect His Secret Identity
Superman is a hypocrite when it comes to the Fortress of Solitude. It is filled with Kryptonian technology that would have massive benefits to mankind, but he hordes it all for himself.
One of these innovations is the Superman robot. Depending on the era, Superman has a team of robot lookalikes that are similar to him in power. He often uses them to deal with situations involving Kryptonite, or other scenarios where it would be too dangerous for him to enter. There also exist Clark Kent robots, whose sole purpose is to help Superman with keeping his identity a secret. The main purpose the robots serve is maintaining and protecting the Fortress of Solitude.
The ability to create loyal robots with powers similar to Superman would be an incredible gift to humanity. Why should there be only one Superman when you could have ten, or twenty, or a hundred. Instead, he uses them to make sure he can keep his lame reporter job a secret.
He Once Disco Danced In Order To Defuse Bombs
One of the big complaints about Man of Steel and Batman v Superman is that they were far too serious in tone. There is plenty of room for levity in a Superman story; not everything has to be weighed down by the relevance and importance of being such an important fictional character.
With that being said, if you go too far into lighthearted stories, you end up with "Super-Disco Fever" from Superman Family #196.
Even thought Clark Kent is supposed to be a nerdy reporter, he inexplicably has a fan club of hot young women. They drag him into a local disco, and force him to judge a "Dance Like John Travolta" competition. As this is happening, Clark uses his X-Ray vision to spot a staff member from a rival disco planting bombs beneath the dance floor. The disco wars had gotten so harsh, only terrorism and mass-killings could determine who truly has Night Fever.
In order to stop everyone in the disco from being blown up, Clark Kent enters the dance competition, and begins disco dancing on the stage. He uses the dance steps to mask the fact that he is using "super-vibrations" to disable the bombs beneath the stage.