The South Essex were a new regiment formed by Sir Henry Simmerson, they were badly trained and badly led when Sharpe, then a lieutenant, was attached to them with some of the 95th rifles. After Simmerson's actions led to the loss of one of the King's colours, the rifles and South Essex became a battalion of detachments. The title of the South Essex was restored only after Sharpe and several of his men captured a French Eagle - at Talavera in 1809. (These are the events of "Sharpe's Eagle")
Command (Below) -
Lieutenant Colonel Lawford & Lieutenants Robert Knowles, Harry Price and Ensign William Matthews.
Lawford was Henry Simmerson's replacement, and Sharpe's 'Friend' since Sharpe kept him alive and Lawford taught Sharpe to read in the Sultan of Tippoo's dungeon (back when Sharpe was just a private in "Shape's Tiger")
He was badly wounded in the breach at Ciudad Rodrigo ("Sharpe's Company") and was succeeded by Colonel Windham, but I like this character, so he remains in command of the South Essex.
Knowles eventually purchased the captaincy of his own company, and was later killed by Hakesewill at Badajoz.... but I have kept him with the South Essex.