Who was the commander of the northern army?

The Union army saw many changes of command. Winflied Scott was the first, but he retired because his health was failing (he was ancient). The George McClellan was put in command. He was replaced with Helleck because of his indesicveness. McClellan was put in charge again and was then replaced by Meade. Grant was put in command for the remainder of the war in 1864.