Rifleman Apolis was "consistently able to raise morale"
A British soldier shot dead while on foot patrol in Afghanistan was described as a "big brother figure" with "natural maturity and wisdom".
The tributes came as the MoD named the soldier, killed on Monday morning, as 28-year-old Rifleman Carlo Apolis.
Rifleman Apolis, from A Company 4 Rifles, was hit by small arms fire near Sangin, in Helmand province.
Another UK soldier was killed in the region on Tuesday, bringing the death toll to 268. He has not yet been named.
'We shared everything'
The MoD says the death of South African-born Rifleman Apolis was not connected to Operation Moshtarak, the Nato offensive in southern Afghanistan.
Lt Col Rupert Jones, Commanding Officer 4 Rifles, said: "Rifleman Carlo Apolis was something of a big brother figure to the younger riflemen.
"He was older than most and others naturally looked up to him and sought his guidance. But it was not just his age that stood him apart, but his natural maturity and wisdom. He was generous to his core."
Rifleman Apolis's girlfriend, Rebecca Williams, said: "Most people will have known Carlo as fun loving and highly entertaining, someone who could make you smile and motivate you when you were feeling down.
"But outside work he also had a much quieter and more reserved side that not many people would have seen, and he liked to keep his personal life private.
"Carlo was my best friend and we shared everything together, I miss him so much and he will always be with me in my thoughts. He will be sadly missed by everyone that knew him."
Lt Col Nick Kitson, Commanding Officer, 3 Rifles Battle Group, said that Rifleman Apolis's calibre had come through after he had been injured earlier in his deployment.
He said: "Wounded previously in this tour of duty, it was a mark of his determination and commitment that he wasted no time returning to his team and continuing with the important work that they are doing here in Sangin."
A tribute was also paid by Secretary of State for Defence Bob Ainsworth.
He said: "I was so very sorry to learn of the death of Rifleman Carlo Apolis and it has clearly come as terrible news to his many friends in the Army.
"Not only was he looked up to by many fellow soldiers as a valued source of guidance, but many of his comrades remember fondly his consistent ability to raise morale.
"My deepest sympathies are with Rifleman Apolis's family and friends at this time."