Have you got a written employment agreement with your employers? If so, then chances are very good the employer owns the presentation, not you, since you likely signed the results and proceeds of all work done while on the job to them.
Even if you don't have a written employment agreement, if you did this in the course and scope of your employment, and it sure sounds like you did, agency and copyright law say that your employer owns the results of your work for them. It wouldn't matter if another manager within the company used "your" presentation, since it's the company that owns it.
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As Ms. Koslyn points out, wihtout a written agreement materials prepared for your employment and paid for through your employment belong to your employer.
The above is general legal and business analysis. It is not "legal advise" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
The presentation itself is copyrighted just because you created it. You could register the copyright, but I don't think it would help you. As an employee, your employer owns the work and can do anything with it, including let others use it.
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You cannot "copyright" it. That copyright went to your company automatically upon your creation of it as an employee of your company and it now belongs to your company, not you. The company owns the copyright as a "work-for-hire." The company can do whatever it wants with it. The only way it would be possible for you to obtain the copyright is if the company agrees to give you exclusive rights to it. While a win might be in the cards for the STL Cards, it's not in the cards for you.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.