Gaalsien is a character referred to in the RuneScape Knowledge Base, in the article "Ranged - Crossbows and Bolts". Gaalsien is not referred to within the game itself, leaving his history and race unknown.
The story briefly describes Gaalsien's fight with a greater demon.
Gaalsien notched another bolt as he prepared for the beast's next attack. It had been a long time since he'd had the misfortune to come across a greater demon, but he was determined not to be found wanting.
With flames bursting from the ground where its hooves struck the splitting earth, the demon was bellowing its rage into the air as it charged. The bolt struck it in the shoulder. Gaalsien had time to consider that such a shot might have slowed a human or a dwarf, but that demons do not obey the rules of this world.
Before the beast reached him he had fitted another bolt - tipped with a glowing gemstone - and raised the crossbow towards the abomination. Down the length of the crossbow's stock he looked into the vast darkness within the demon's eyes. There was an emptiness there, and it was into that emptiness that he fired, knowing that this shot - flawlessly aimed and prepared - would unleash the spell dormant in the gem.The demon stopped its charge, faltered as the spell tore its unholy life from it, and dissolved into ash.