The highest rank in Army is that of

Brigadier
General
Lieutenant General
Major General

The correct answer is: General.

A General is a commissioned officer of the highest rank in the armies of many nations. In the United States Army, a General is a four-star officer, with the rank insignia of four stars on the shoulder boards. Generals are typically in charge of large military units, such as divisions or corps.

A Brigadier is a commissioned officer of the rank immediately below that of Major General. In the United States Army, a Brigadier is a one-star officer, with the rank insignia of one star on the shoulder boards. Brigadiers are typically in charge of smaller military units, such as brigades or regiments.

A Lieutenant General is a commissioned officer of the rank immediately below that of General. In the United States Army, a Lieutenant General is a three-star officer, with the rank insignia of three stars on the shoulder boards. Lieutenant Generals are typically in charge of large military units, such as divisions or corps.

A Major General is a commissioned officer of the rank immediately below that of Lieutenant General. In the United States Army, a Major General is a two-star officer, with the rank insignia of two stars on the shoulder boards. Major Generals are typically in charge of smaller military units, such as brigades or regiments.