Marilen is a woman from Tora and the current palace librarian. She was originally believed to be Lief's fiancée, but is actually his distant cousin and the former heir presumptive to the Kingdom of Deltora.
Although she was not mentioned specifically, Marilen was among the hundreds of Torans who broke their vow to Endon and were swept away to the Valley of the Lost to become the Guardian's subjects. She was freed with the rest of her tribe when Lief, Barda, and Jasmine defeated the Guardian.
Lief and Doom met Marilen in Tora and brought her to Del in secrecy. Rumours of her arrival quickly spread through the city. Most of the population, including Jinks and Jasmine, believed she was to be Lief's new bride, as taking a Toran spouse was the custom of the royal family. Lief gave her the Belt of Deltora to wear when he, Barda, and Jinks left to follow Jasmine and Glock to the Os-Mine Hills.
To minimise public knowledge of her existence and reduce the possibility of an attempt on her life, Marilen was forced to remain in the upper levels of the palace. She frequently visited the library to talk with Josef and Ranesh, eventually growing feelings for the latter. Josef quickly noticed these feelings and sent Ranesh away on some errands.
One day, Marilen noticed the Amethyst dull when she received her usual tray of food, alerting her to the presence of poison in her meal. She left to tell Sharn of the discovery, and the two discovered Jinks' corpse in Marilen's room after he ate the poisoned cake intended for her. Marilen and Sharn discussed who could have poisoned her. At first, Sharn suspected Ranesh and Marilen suspected Josef, but after further investigation Sharn realised it was Amarantz.
After Sharn stopped Amarantz from poisoning Doom, Steven, and Lindal, Marilen came into the kitchens and angrily stated that she refused to be isolated anymore.
Marilen greeted Lief, Barda, and Jasmine upon their return to the palace. She gave the real Belt of Deltora back to Lief, and he informed his companions that Marilen is his cousin and heir. Marilen told Lief, much to his incredulity, that everyone believed she was to be his bride.
Marilen was among the party that found Lief and Barda in the Dreaming Dunes. She might have been one of the one hundred Torans who freed Veritas from the sand. Later, she informed Lief that his mother had returned to Del shortly after they learned of the companions' location.
Upon Sharn's return to Del, Paff began spreading the Toran Plague throughout the city. She also distributed notice flyers labelled the "Toran Plague" and "Toran Plot." They falsely claimed that the plague was sent by the people of Tora to ensure Marilen would become queen. Should King Lief die, Marilen would become the ruler and Tora would become the capital of Deltora.
Lief learned later that the plague was actually poison applied in ways that made it resemble a plague. He had Zeean write a letter to Marilen, informing her of what was happening. Later, believing he would not be alive much longer, Lief sent Ranesh to bring Marilen to Del so she could claim the Belt when Lief died. Marilen arrived after Fidelis destroyed the Sister of the South, bringing food from trading ships that have come to the Bone Point Lighthouse.
Marilen attended the wedding of Lief and Jasmine. She later documented the wedding in the Deltora Annals and took up the position of palace librarian after Josef's death as Ranesh was now Lief's advisor. Marilen and Ranesh had a son, whom they named Josef. With the birth of Lief and Jasmine's daughter Anna, Marilen is no longer Lief's primary heir.
When Marilen is first introduced, she appears to be timid and quiet, a dutiful daughter of Tora. However, after she goes to live in the palace in Del, she grows in confidence and poise, so much so that Sharn is surprised at how strong-minded and confident she has become in such a short amount of time. She has the courage to stand up to Doom and demand that she not be hidden away like a prisoner but be allowed to venture onto all floors of the palace.
Marilen first met Ranesh when she came to Del to wear the Belt should Lief die on his quest to save the trapped Deltorans in the Shadowlands. They fell in love and married after the end of The Shadowlands. They have a very loving relationship.