Short answers, pulled from the story.
The King's Royal Rifle Corps traces its foundation to 1756, when Parliament passed a special act on the 4th of March 1756 creating four battalions of a thousand men each for service in North America. Royal approval and funds were granted just before Christmas 1755, which is why the regiment's traditional birthday is Christmas Day.
The regiment was raised in response to General Edward Braddock's defeat in 1755, which exposed the unsuitability of conventional British troops for forest warfare in North America. The new regiment was designed to combine colonial and foreign legion characteristics, recruiting Swiss and German forest-fighting experts alongside American colonists to better counter French and indigenous forces.
Celer et Audax is Latin for Swift and Bold. General James Wolfe is said to have granted this motto to the 60th Regiment of Foot at Quebec in September 1759, following the regiment's service in the campaign that brought Canada under British control.
Henry Bouquet was a Swiss citizen who served as commanding officer of the 1st Battalion of the 60th Royal Americans. He introduced the rifle informally and developed practical clothing for bush-fighting, ideas that were well ahead of their time. He also led the regiment's detachment to victory at the Battle of Bushy Run in August 1763 during Pontiac's War.
The 1st Battalion deployed to North Africa and fought at Sidi Rezegh, El Alamein, and in the Italian Campaign, with Rifleman John Beeley earning a posthumous Victoria Cross during Operation Crusader in late 1941. The 2nd Battalion was lost in the defence of Calais in May 1940, reformed later that year, and eventually fought through to the end of the war in North-West Europe, finishing six days after VE Day.
The King's Royal Rifle Corps was formally amalgamated with the Oxfordshire and Buckinghamshire Light Infantry and the Rifle Brigade in 1966 to form the Royal Green Jackets. The merger process began in 1958, when the three regiments were grouped into the Green Jackets Brigade, and the KRRC was re-titled the 2nd Green Jackets.