Who was the commander general of the northern troops during the civil war?

There were four Generals-in-Chief of the Union armies - in this order.

First, Winfield Scott - a highly prestigious leader, who correctly predicted that it would be a long war and suggested an appropriate strategy, but far too old for the job.

Second, George McClellan - energetic and efficient, loved by the rank-&-file, too inclined to wait till everything was ready, and mistrusted on this account by some in Lincoln's cabinet who doubted his loyalty. (He ran against Lincoln in the '64 Election.)

Third, Henry Halleck - a respected intellectual who believed in occupying territory, rather than pursuing and destroying armies. The territories were far too big to occupy, and his campaigns lost vital momentum. A chilly personality, generally unpopular and guilty of much feuding.

Fourth, Ulysses Grant - a basically simple man who was good at simplifying problems. When he moved into the top job, he simplified the situation with alarming directness. The Confederates were running out of recruits. So he ended the system of prisoner exchange and conducted a war of attrition - at a huge cost in casualties, and appallingly overcrowded prison camps - until the enemy lines simply broke.