Resistance: Fall of Man
Captain Buckler is revealed in an Intel entitled Spires. He was found by a solider on patrol outside of Exeter and the soldier that found him made the following observations. He had been on his own for quite a while and when brought back to civilisation, he wasn't very talkative and managed to eat a day's rations in about five minutes.
Two days later he started to come around and this is when they discovered his name was Buckler. It appears that he was there when the Chimera took Salisbury. They had set up a large fortified field, trenches, tanks and so on. However, Spires were deployed and they were soon over run with Crawlers. Salisbury was decimated and it's assumed by the Soldiers that found Buckler that he ran. They don't blame him, and they only come to this conclusion as he won't tell them how he survived.
After his rescue he headed back to Southern Command. He escaped to Cardiff when Southern Command was overrun, but was killed in action when the last remaining soldiers launched an assault on the tower in London.