Brick wall is a term applied by genealogists and other family historians to a relative whose details are largely unknown, with no apparent way of enlarging the data.
Familypedia is a good site for showing what is known of such elusive relatives. Create a separate page for that person, with all the detail you know about spouse(s) and children, with dates and places, and use the "notes" sections to recount anything else that might be just family tradition or might be true. Because of the way our pages get indexed by Google and other search engines, you will have increased the chance that someone who knows more about the person will see it on a web search and contact you.
You can also use the county "talk" or "query" pages if you know which county (or similar area) the "brick wall" spent some time in.