Edit - Old Abe, the mascot of the 8th Wisconsin, was named for Abraham Lincoln. The mascot was nicknamed War Eagle, but I can find no source indicating that that nickname was ever applied to Abraham Lincoln.
... I wanted to add that of course I know the story of "Old Abe" too, the famous war eagle of the 8th Wisconsin Volunteer Infantry. But in his case I thought the nickname was "Old Abe" while in my first story the nickname of the eagle named Anvre was "War Eagle". I have a hunch that "Old Abe" may have been the right answer, or better the answer that was sought for, but will stubbornly cling to my first post ... not because I don't know this story, but because I find the other story more fitting to the question
(and I know I will probably pay a price for being stubborn ...)
Oh, btw, @ami , where is the "Delete" button? The other day I had hit "Post reply" accidentally while I was in the midst of answering. Normally I would have deleted that crippled post and written a new one, but that seems no longer possible?!
Edit - Seddon served longer than anyone else in the post of Confederate Secretary of War, but I can find no source indicating that nickname of War Eagle was ever applied to him.
Answer: Nathan Bedford Forrest. Is the Answer I was given, however, it seems this was not a cut and dry question. @hoosier it is up to you how to score.
Edit - In addition to Forrest, I am accepting answers of Robert Milroy, Eugene Asa Carr, Old Abe the mascot of the 8th Wisconsin, and the Auburn University mascot who supposedly was discovered on a Civil War battlefield.