Hamlin

From the Resistance Wiki

Sgt. Hamlin is the first known person to take a Stalker down single handedly.

He and his squad patrolled Manchester, England and, when almost all of the British Resistance aircraft were shot down, the Stalkers began to kill ground forces in the city. When one Stalker ambushed his squad Sgt. Hamlin ran around the back of it and concentrated his fire on its power core, which destroyed the Stalker.

The Intel with this information was found with a dead soldier in the trench near the children's play park, so it is probable that Hamlin and a few of his men were killed gruesomely but kind of comically on the play equipment.