The first time he saw the sight of seafoam mixed with blood was when he found himself at the wicked end of a blade during the First Kinslaying at Alqualondë. Since then, Alagosdil has found himself embroiled in a deep bitterness towards the Deep Elves, and he considers the fact that he survived on that terrible day as both a mercy and a curse. Since then, he cannot stand to look at idle waves too long, where the seafoam becomes murky and stagnant, and he much prefers the roaring waves of the deeper ocean and its unpredictability.

One of the few remaining Falmari of Alqualondë, he is one of the even fewer who took up arms alongside the Host of the Valar to assist in fighting in the War of Wrath. While there, although horrified by the losses of war, including that of his sister, he was also enraptured by the beauty and mystery of Arda. With the Drowning of Beleriand only deepening the distance from his home and all he had left behind, he made his way to Lindon and settled among the Falathrim under the Lord Círdan. It was not long after this that he made the acquaintance, and later friendship, of Lothulien.

It was in Lindon that he adopted the name of Alagosdil, for his love of the deep, wild ocean was made plain in the days, and even weeks he would spend long out at sea; even when there were those who would protest his ventures and warn him of coming storms and winds, there was little that could be done to stop him once he had set his mind to journey and exploration. In time, he and Lothulien took to journeying together, and so they would sail down the coast of the Ennorath and spend centuries exploring the lands of Arda; Alagosdil promising guidance by following the stars, and Lothulien quietly sketching out a map of their journeys so they would not find themselves hopelessly lost.

When came the time of The Last Alliance, for men and elves to band together against Sauron, Alagosdil was, at first, one of those who openly raised sword and shield against the forces of the Shadow. But as the war wearied on, and he began to grow embittered once more by the ever-present vanity of the Noldor, and his mind drifted back to elder days where he risked life and limb for a fate that was not of his own making, his willingness to fight dwindled. After Oropher's folly of a charge that incurred the slaughter at Dagorlad, Alagosdil fled. He abandoned his post, and put up his sword, and slipped away into the night, leaving naught but a gentle ripple in his wake as he went.

Although in recent days he speaks with no pride about his desertion, and in fact speaks little of it at all, one would be hard-pressed to find the residual jadedness of a warrior long haunted by blood and battle. Alagosdil laughs loud and boisterously, and he demands attention in stride and tongue, and he tempts to make new crafts that would rival the vanity of those whom he claims to hate. Yet his deepest love remains his ship, and the sea, and when the sun sets over the long horizon and he is left alone beneath a starry sky, it is only then he knows peace.