Do antivirus companies create computer viruses?

No. Antivirus companies know the risks involved when dealing with computer viruses and the potential dangers of viruses getting out in the wild. Antivirus companies do not hire people who've made viruses, and the whole concept of antivirus companies creating viruses is simply a myth, urban legend and conspiracy theory.

But, creating viruses helps increase antivirus companies profits.

There are plenty of viruses and other malware to justify the needs of antivirus programs. If antivirus companies really believed that distributing viruses would help increase profits or sales, they would create viruses and other malware for other platforms.  Such as the Apple Macintosh and *nix where virus threats are not as high with Microsoft Windows users.

Antivirus companies are able to maintain and increase their products by staying up-to-date at detecting, and cleaning all computer viruses and other threats.

Where is your proof that antivirus companies don't do this?

1. Creating computer viruses is not that difficult for someone who's familiar with computers and programming. Creating viruses would not help in the detection or prevention of viruses.
2. An antivirus company couldn't protect itself from the virus before it was released without raising suspicion. Therefore, it would infect its own product, causing customer dissatisfaction.
3. There are plenty of other users who are not affiliated with antivirus companies who already do this.
4. The code that makes up a virus is reviewed by dozens of security experts when a virus gets out in the wild. Analyzing that code could trace its origins back to the antivirus company.
5. An antivirus company could be held liable for creating viruses, which would not only make the company look bad but could cause a lot of lawsuits.