Saber is the love interest of Shirou Emiya in the first route of the visual novel Fate/stay night and the main love interest of the first anime adaptation.
She is Shirou's Servant, an agile but powerful warrior. Loyal, independent, and reserved, Saber acts coldly but is actually suppressing her emotions to focus on her goals. Her class is considered the "Most Outstanding," with excellent ratings in all categories. Since her Master cannot effectively provide her with mana, she minimizes her activity to preserve what she has. Saber is frustrated by Shirou's "protective" tendencies, believing his erratic and reckless behavior will jeopardize her chances of winning the Holy Grail War.
Her true identity is that of King Arthur aka. Arthur Pendragon (Uther's daughter who hid her gender to be accepted as King). She has joined the Holy Grail War in order to grant her wish of redoing the selection of King due to her belief that she failed to keep her country from chaos. She wields the legendary holy sword Excalibur (cloaked in a veil of wind to hide its popular identity and thus its owner's) but no longer carries its lost sheath Avalon.
Saber is a strong-willed young woman who always speaks resolutely. She is courageous, determined, and set on winning the Holy Grail. She constantly insists that she is a knight first and that her gender is of little importance to her. She is resolute in following her own morals regardless of more viable tactics being available should she consider them to be underhanded, leading to conflicts with Kiritsugu over the strategy within the Fourth Holy Grail War. While obtaining the Holy Grail is of the utmost importance, rejecting her chivalry is something that she will not do under normal circumstance even if it should put her at a disadvantage.
She doesn't like to be treated as a woman, or even as a human, due to her status as a knight and a Servant. She tries to keep the notion that she is only a Servant, a tool for her Master, first and foremost in her mind, so she initially has no objections about Shirou accidentally seeing her naked body. She slowly becomes more aware of herself after their relationship develops, and eventually even becomes flustered upon the same situation being repeated. She is unwilling to show emotions, as she has suppressed them so strongly and views herself as a knight foremost. Even though she attempts to hide them, her insecurities become more and more apparent, and she later begins to open up more and show her emotions more easily, especially to Shirou.
Though she once felt more linked to dragons, she came to enjoy lions after taking care of a lion cub for a month at some point in her life. She claims that it is not that she "likes" them, but rather the happiness she experienced as he became attached to her brought forth a bond with them. He was very energetic, often biting or scratching, but she wished to be able to stay with him until the end. She has had feelings for them since then, and even remembers the fond memories while holding a stuffed lion. Shirou seeing the memory of her rubbing her cheek against the lion comments on it being a time where she looks like a girl her age.
She is shown to have a humongous appetite, finishing large servings of rice within one minute. Although she can normally eat anything, Shirou's food education is what awoke her gourmet spirit. She originally did not appreciate modern food as she doesn't actually need to eat as a Servant and because she had believed that all food was like fish and chips. She had very bad experiences with the food in her time, due being limited to meals like large quantities of potatoes, vinegar, bread, and ale or even at times simply eating vegetables alone.