Arthur Watts is a former Atlesian scientist.
Arthur Watts is a member of Salem's group.
Not much is known of their relationship, but Watts is loyal and respectful toward her. Despite this, his faith in her is not absolute, as shown in "So That's How It Is", when he doubts Salem's claims that Cinder Fall is still alive. However, a stern look from Salem makes him reconsider his disbelief.
There has been very little shown interaction between the two, but when Salem asks Watts to have a new tail made for Tyrian following his loss to Ruby Rose, he takes no issue with the request and sets out to perform it.
Later, when he questions Salem on Cinder still being alive, Tyrian immediately calls him out, making him stammer for a moment before he regains his composure.
He is next seen calling for Tyrian in "Lost", saying it's time to disembark on their mission to Atlas.
At first Watts is relieved to hear of Ozpin's death in "The Next Step". But when Hazel Rainart reveals he is taking the Relic to Atas, Watts is not surprised, apparently knowing of Ozpin's ability to reincarnate. However, he also knows that Ozpin could get into Atlas, considering his connection to General James Ironwood.
Professor Lionheart is Salem's mole in Mistral, and an important pawn in her targeting of Mistral. Arthur serves as the representative of Salem to Lionheart. Watts currently appears to treat Lionheart with civility but also occasional playful condescension.
As one of Ozpin's most trusted allies, Qrow is a primary target of Watts, who does not in any way underestimate the renowned Huntsman's strength and tenacity in combat. Due to this, Watts is extremely wary of Qrow's abilities and has no desire to engage him head-on.
The two have not been shown interacting as of yet, but when the news of Ozpin's return reaches Salem, Watts and Tyrian are ordered to deal with Ironwood so he does not undermine their plans for Vacuo.
Watts looks down on Cinder after she was thwarted by Ruby. He greatly enjoys tormenting and angering her, especially since she is unable to respond following her injury. Given his comments, they apparently had a preexisting rivalry prior to her injury as well.
In "Dread in the Air", he has a disappointed tone after discovering that Cinder's voice has recovered. In "A Perfect Storm", Watts works with Cinder to pressure Raven Branwen into having Vernal use her Maiden powers to open the Relic of Knowledge's chamber. When she agrees to the bandit's demand for her brother's death, Watts warns Cinder of her intentions to get revenge on Ruby; however, she dismisses him and burns his hand in response.
His disbelief to Salem's claims in "So That's How It Is" implies that he believed that Cinder perished in Haven.
Watts treats both Emerald and Mercury with disdain, derisively calling them Cinder's "posse".
Upon finding and meeting Raven Branwen in "A Perfect Storm", Watts is professional in front of her but pressures her into cooperating with Salem. However, he disagrees with her terms for luring her brother into his death because of the risks of exposure and putting the Kingdom on high alert.