Called "the greatest hero of the Civil War," Grant's the kind of leader we would want if things with the aliens got ugly, guaranteeing victory after victory with the strategic mind that brought the South to both a military and economical defeat way back in 1865. As historian Michael Korda put it,
Grant understood topography, the importance of supply lines, the instant judgment of the balance between his own strengths and the enemy's weaknesses, and above all the need to keep his armies moving forward, despite casualties, even when things had gone wrong-that and the simple importance of inflicting greater losses on the enemy than he can sustain, day after day, until he breaks. Grant the boy never retraced his steps. Grant the man did not retreat-he advanced.
Plus, he's called US Grant. For symbolic purposes alone, that can't be beaten.