Short answers, pulled from the story.
The Army of Northern Virginia was led successively by P.G.T. Beauregard, Joseph E. Johnston, and Robert E. Lee. Johnston commanded from the 20th of July 1861 until he was severely wounded at the Battle of Seven Pines on the 31st of May 1862. Lee led the army from the 1st of June 1862 until the surrender at Appomattox on the 9th of April 1865.
General P.G.T. Beauregard created the army's distinctive battle flag because the Confederate national flag, the Stars and Bars, was too easily confused with the Union flag in the smoke and chaos of battle. The new design spread to all corps and forces under the army and became its primary battle symbol throughout the war.
The Army of Northern Virginia surrendered on the 9th of April 1865, when General Robert E. Lee signed the papers of surrender to General Ulysses S. Grant at Appomattox Court House. On the 10th of April 1865, Lee issued General Order No. 9 dismissing all troops on their word of honor, and 28,231 soldiers were formally paroled under that order.
The army's peak strength reached 82,633 soldiers during the Richmond-Petersburg Campaign. At Gettysburg in 1863 it fielded 75,054 soldiers. By the 31st of January 1865-69,659 were fit for battle, though more than 4,500 of those had no rifles.
J.E.B. Stuart commanded the army's cavalry, which he organized into a full division on the 17th of August 1862 and which grew into a corps by the 9th of September 1863. Stuart led the corps until the 11th of May 1864, the day he was mortally wounded. Lieutenant General Wade Hampton III then took unified command on the 11th of August 1864.
The army was officially renamed the Army of Northern Virginia on the 14th of March 1862, reflecting its primary geographic area of operations. The name also derived informally from its parent administrative structure, the Department of Northern Virginia, which General Joseph E. Johnston had commanded since the 22nd of October 1861. Robert E. Lee's biographer Douglas S. Freeman credits Lee with settling the name when he assumed command on the 1st of June 1862.