You already have copyright in it (unless you created it for someone else, as part of your employment or as a commissioned work, in which case the employer should have copyright). Unlike patents, copyright inures in the act of creation--the creator of an original graphic work has copyright simply by virtue of creating it. You can and should assert copyright, by stating someone on or near your work (e.g. on the website) that it is "Copyright whatever year John Doe."If someone misapprorpriates your work, you can bring a legal action for damages and to stop them.There are ways to enhance your protection of the character, such as by registering the copyright (which should cost much less than $5,000), trademarking it, or *possibly* looking into a design patent, though patents tend to not apply to graphic characters.So, as stated, you can already assert a basic level of copyright protection; you may also, in some contexts gain additional protection from unfair competition law. To understand the extent and limit of your protection, as well as to explore options for how to better protect your work, you should consult with an intellectual property attorney.