Lissuin Tillon Tarthir is what is called a 'havenborn'[1]: the child of a couple who met in the Havens of Sirion during the final days of the First Age. In his case, his father was a Noldo of Gondolin, a minor member of the House of the Golden Flower; his mother was a Sinda of Doriath.
Tarthir was born in Lindon, early in the Second Age. Adopting a Noldorin tradition,[2] his parents each chose a name for him. His father named him Lissuin, after the fragrant flower of Tol Eressea and in token of his descent from the House of the Flower; his mother named him Tillon, after Tilion the archer of the moon and patron of the Sindar. Before he was out of childhood, he picked up an epesse which became his most commonly-used name: Tarthir, the stiff-faced.
Tarthir was raised in his parents' lodging-house in Mithlond. In Gondolin, his father had run an inn named I Soron[3]; in married life, he founded a successor, named in Sindarin as I Thoron a Chên.[4] The couple catered for Elven visitors from across Middle-earth: Eregion, Lórinand, Eryn Galen, and of course Lindon itself. Growing up, Tarthir was exposed to every Elvish language spoken in Middle-earth, and became conversant in all of them.
He also became familiar with the customs and cultures of his parents' visitors. Indeed, this became his main occupation: to set guests at ease by making sure their own cultural traditions were followed in I Thoron a Chên. His facility with language was a great help in this role.
And yet it was also wearing. Once the Numenoreans began to settle in Middle-earth, and especially after the fall of Ost-in-Edhil to Sauron, increasing numbers of the inn's guests were waiting for ships to the West, and Valinor. Tarthir began to grow tired of meeting new and interesting people only to see them walk over to the docks and never return - and began to wonder, given the darkening state of the world around him, whether they might not have the right idea.
At last came the Fall of Numenor, the change in the world, and hot on its heels the War of the Last Alliance. Tarthir's parents were crushed by the death of Gil-Galad, and openly discussed taking ship themselves; but in the end they chose to stay, and help others who were making the journey.
Tarthir stayed too - for a while, to see if things had improved. But when word came of a Shadow returning in the east, and when the arrival of messengers from the West in the year 1000 was heralded by the coldest winter Mithlond had ever seen[5], he had had enough. Bidding farewell to his parents, he took ship and sailed the Straight Road to Tol Eressea.
Shortly after he landed, he encountered a blonde Vanya named Coirelótë. As Tarthir was one of the only people around the docks who could speak Quenya to any degree, she immediately latched onto him.
Coirelótë had a much less exciting life than Tarthir. Born in Valmar of the Bells to a Vanyarin couple early in the Third Age, and named for the early spring blossoms of the peach tree, she had for the past couple of yeni wandered around Valinor, meeting new people and seeing new places. Her travels had finally brought her to Tol Eressea, but she discovered on landing that her knowledge of Quenya (Vanyarin and Noldorin) and Telerin was almost entirely useless on an island where the common tongue was Sindarin - a language never spoken in Valinor proper.
It could have been luck or fate that brought Tarthir and Coirelótë together, as each stepped off their respective ships onto the docks of Avallone. She wanted to experience the cultures that had originated in Middle-earth; he was an expert in those cultures, but only wanted an easy life. Right there in the harbour, they made their agreement: Tarthir would act as translator and guide for Coirelótë, and in return Coirelótë would attend to all the details of housekeeping and food that he would rather not think about. It worked quite well, all things considered.
[1] This term and concept invented by Huinesoron, but there would have been at least a few of them around.
[2] Stated in LaCE as just an Elvish thing, but as Philosopher@Large noted a couple of decades ago, there are no instances of non-Noldorin elves with separate mother- and father-names.
[3] 'The Eagle'.
[4] 'The Eagle and Child'.
[5] I read this idea in a fanfic many years ago - when Cirdan surrendered the Ring of Fire to Gandalf on his arrival, what would the impact have been on Mithlond's climate?
hS