Ruth Leonidas was a citizen of "Atlantis", in truth an altered form of Earth in some timeframe, and a priestess of the temple of Poseidon, who became a companion of Bernice Summerfield when she found herself stranded there.
Despite her calling, Ruth was secretly a "historian", someone who wanted to uncover the truth beyond the rule of the Great Leader, the entity that seemingly ruled Atlantis, who had outlawed any kind of history before Year Zero. Alongside Leonidas, Ruth helped Bernice begin to understand just what was going on around her, and the two became close friends after they defeated and destroyed the computer that Poseidon, aka the Great Leader, actually was. (AUDIO: The Temple of Questions)
They tried to protect Benny from retribution against their act against "the gods", only to be captured by the minions of the Epoch, the powerful entities behind what was really going on. Due to her spending time with Benny, and their questioning of the status quo, Ruth became immune to the memory reprogramming that was commonly performed by the Epoch amongst the populace. This helped her see the changes to reality that were going on around Atlantis, before she and Benny were captured by the Epoch. (AUDIO: Private Enemy No. 1)
When confronted by the Epoch, she and Benny were forced to decide who among three versions of themselves were actually real, and witnessed the death of one Benny and the almost demise of herself, until Benny switched that reality "off". Before they could decide any further, Ruth began to remember moments from her "real" life, and grew very confused at the new memories and her existing ones. She then met another version of herself who had been stuck in Victorian England at the mercy of an alien who had taken the identity of Spring-Heeled Jack and was scaring the locals (with whom this Ruth had become quite taken). Although they sent her back to that reality, they were unsure if she survived the journey due to the gateway closing prematurely.
When Benny made the decision to erase their "reality", in order to stop the Epoch from interfering anymore, Ruth seemingly sacrificed herself to secure Benny in an emergency hibernation unit, arguing that Benny had more to live for, with a son waiting for her somewhere in space and time. (AUDIO: Judgement Day)
However, much to her surprise, she woke up on an alien world, in the 27th century, and tried searching for Benny, to no avail at first. Taking the name Leonidas as a surname, in tribute to her friend Leo, who had been taken over by the Epoch, she journeyed to the planet Lyndyaz. There, she found that Benny had somehow become part of their religion as a minor deity of sorts. She took up an archaeology class and was hired by the professor as an assistant. When he began work on a dig into a new site, she advised him to recruit an offworlder, hoping it would attract Benny's attention and bring her to Lyndyaz. (AUDIO: Brand Management)
After this she accompanied Benny to Legion. Along the way she became a nun so that they could get the co-ordinates of legion. She couldn't sing and didn't like all the snooping to get there. She helped Marianne to discover who was behind the recent murders. (AUDIO: Bad Habits) She also was resourceful when the taxi that was taking them to Legion crashed, and she helped protect Benny and the others from Sand Roaches. She couldn't come to terms with the relationship between the human Dr Carol Bauer and the Killoran Yukon 9. (AUDIO: Paradise Frost)
When on Legion, she helped Peter Summerfield and Benny to explore the Vesuvius. She couldn't understand why Benny didn't like Irving Braxiatel. When she saw a dead body, she became sick. She noticed the discrepancies on the data for the cryo chambers, helping discover who committed the murder of Sheira Rynn. (AUDIO: Vesuvius Falling) She found Dorian Gray's portrait in Triptic House, and thought that the painting was looking at them. She was also the first to experience visions, when Jack made them participate in a seance around Dorian Gray's portrait. (AUDIO: Shades of Gray) She later wanted to know of Peter's boyfriend Antonio Tulloch. She wanted to be friends with him, and knew about the Deindum War. She found out that Antonio wasn't what he seemed. (AUDIO: Everybody Loves Irving)
In a simulation from Benny's mind, when she was in Atlantis she was worried about not fitting in. This simulation then later helped Benny defeat simulations of her enemies from her memory. (AUDIO: Many Happy Returns)
She joined Benny and Jack on the Iverfield on a post run. When they landed on Nemeqit they thought it was just a dead planet. She helped Benny discover the truth behind the missing people. She later swallowed a lot of dust. She realised that if there was an apocalypse people would remember the essential basics, but they wouldn't remember the rituals and the religions. (AUDIO: A Handful of Dust)
She confronted Peter about the fact that Antonio wasn't real, which Peter thought was ridiculous. Avril Fenman later reminded her about her past life, before the Epoch's rewriting of time and memory. Ruth was part of a high class family who looked down upon the common people. During an uprising, Ruth killed her father and then asked her loyal servant to take credit, making her servant into a hero. She then asked that her servant kill Ruth's childhood friend in order to fake her death as Ruth made her escape from the planet. Learning this about her past made Ruth uncomfortable, but she eventually came to terms with it, realising that her present self was her new identity. (AUDIO: The Curse of Fenman)
She accompanied Benny to Saravas as part of her entourage. She ended up doing the tea run by accident for Shepton Rothwell, which she despised. She was persuaded by a possessed Shepton that Jack and Benny were in a relationship. She became paranoid and thought that Benny wanted to kill her. She left Benny when the Epoch arrived. Benny forgot her. (AUDIO: Big Dig)
She was taken by the Epoch as they thought she was what was causing the temporal instabilities around Benny and took her to their domain. She was then brainwashed into thinking she was an actor, called Ayesha Antoine, playing herself and a character called Brook. Benny managed to undo the brainwashing and defeated them. She then used the Epoch technology to find Leonidas. (AUDIO: In Living Memory)