"There's only one person I fight for since the moment we met."
Lucas is the name Dorothy gives an amnesiac man she saves from certain death. His true name is Roan.
In the world of Emerald City
"Whatever you've done, however many you've killed, whatever unthinkable horror you perpetrated... Your mind has done the same thing back - made it unthinkable."
—Mombi to Lucas
He says he doesn't remember anything, neither his name nor how he ended on the cross. He wants the Wizard to help him get his memory back. It's Dorothy that names him 'Lucas' which is the first name that comes to her mind.
He carries a sword of a Wizard's guard but does not recollect if he took part in the massacre of the village Nimbo as a soldier or defected. He possesses a violent streak, which was evident when he killed the witch Mombi.
Dorothy is willing to part her ways with Lucas, but they both end up at the castle of East, with Dorothy posing as the witch's pupil. After being asked to turn down his weapon by Sullivan, Lucas expresses his concern that he is not able to protect Dorothy from danger. Lucas is then distraught when Dorothy performs the Elements ritual and is taken away by the tornado.
When Dorothy returns from the place in-between unable to placate the weather, Lucas defends her against Sullivan and is almost killed. Dorothy pleads for his life and together they escape from the castle.
Lucas and Dorothy encounter a mysterious girl named Silvie in the forest. The girl seems to know Lucas from the past and is unwilling to leave his side, even though Lucas initially treats her in a distant way.
When Dorothy risks her safety to get Silvie home, Lucas is furious at her bravado and admits he cares for her. While helping Silvie, they both encounter Eammon in the village. It turns out that Eammon knows Lucas and calls him by the name 'Roan'.
Later, Dorothy shares her music with Lucas and they kiss.
Lucas and Dorothy are separated, with Lucas and Silvie being taken by Eammon to Emerald City in secret. Eammon used to be Lucas/Roan's commander and he doesn't believe Lucas committed crimes he is accused of.
When Silvie senses Dorothy's presence in the city, Lucas looks for her. He and Silvie get stopped by the Wizard's Guards and Lucas fights them off, killing most of them. He stops when one of the guards, Toby, admits to knowing him and seeing him kill Wizard's men in Nimbo.
Shocked that he's truly a monster and can hurt those he cares for, Lucas turns himself in.
Determined to get his memories back, Lucas is willing to undergo torture. Anna's investigation reveals his memories are magically blocked, not repressed.
West uses her magic to determine that it was Glinda who locked Lucas' memories. Using Lucas' feelings for Dorothy, West manages to unlock some of the memories.
Lucas/Roan was transporting young witches, including Silvie when he was stopped by the Wizard's Guard. The threatened witches reacted by subduing some of the guards with magic and Lucas fought the rest of them off, but was wounded by Toby. He ordered the witches to run and took a pill to erase his memories.
His life now threatened by the Wizard, as he's been found the spy for Glinda, Lucas is freed by Elizabeth. The councilwoman is acting on Glinda's orders and procures a wagon for Lucas to escape in. Lucas finds Silvie to take to Glinda and Dorothy joins them on the trip.
Lucas, Dorothy and Silvie stop by an abandoned farmhouse on their way to Glinda. There, Dorothy and Lucas spend a night together and he assures her he will always be by her side.
When they meet Glinda, she is happy to see both Silvie and Lucas, whom she calls Roan and kisses him. The kiss returns him his lost memories: he no longer feels loyalty to Dorothy, instead he's bond to Glinda and want to join her on their quest to overthrow the Wizard.
Lucas finds himself torn between Glinda and Dorothy, not fully back in his Roan persona. He helps Dorothy deliver Noa's baby. When Dorothy tries to murder Glinda, he intervenes and states that Dorothy would have to kill him first. However, he doesn't chase after Dorothy afterwards, which angers Glinda. Glinda gives him a knife and orders him to kill Dorothy to free himself from her spell.
In the works of L. Frank Baum
Dorothy finds Scarecrow in a corn field while walking along the Yellow Brick Road to the Emerald City.
Scarecrow joins her quest as he wants the Wizard to give him brains. Disemboweled by the flying monkeys, he reanimates once his clothes are filled with straw.
He becomes the king of the Emerald City once the Wizard leaves in a hot-air balloon and rules wisely for a longer while. After being deposed by general Jinjur, he escaped along with Tip and Jack the Pumpkinhead to Tin Woodsman's castle. He managed to get rid of JinJur with the help of field mice, who scared Jinjur away and was later tasked by Glinda to find a lost princess of Oz, Ozma.
After Ozma was found, Scarecrow stepped down from his role as a king and went on to live with Tin Woodsman.
His love interest in the books was a patchwork girl called Scraps.