Arthur Watts is a former Atlesian scientist that was disgraced due to a disastrous incident, the exact circumstances are currently unknown but from Watt's own words it seems that General Ironwood seemed to have played a role in it.
Prior to him faking his death and his being disgraced from the Atlesian military and scientific community, Arthur seemed to have been one of Atlas' leading scientific minds, as he himself has stated to have invented and assisted in developing and creating the security systems of the Kingdom's two major cities Mantle and Atlas and was later seen having worked together with Pietro Polendina in its defensive military technology development.
However despite all of his service in developing the kingdom, it has been implied by Arthur himself that he never had much loyalty or care for Atlas in the first place, as he had created a secret back door into the kingdom's security system for his personal use and later upon being disgraced from Atlas, Arthur has shown little to no remorse in now actively assisting and aligning with Salem in her plans to destroy the kingdoms of Remnant and obtain the Relics, as seen when he assisted Cinder and her faction by creating a virus to infiltrate and control the Vytal Festival selection system's and take control of Atlas drones during the Fall of Beacon to attack Huntsmen and innocent civilians to further slander Atlas and has now begun actively working on completely destroying the Kingdom together with his associate Tyrian Callows in order to advance Salem's agenda.
Arthur Watts is a member of Salem's group, having provided Cinder the virus to rig the Vytal festival and hijack the Altas drones. While, why he sided with Salem is not entirely known, it's implied that he joined out of spite of Ironwood and Atlas.
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.
In "The Enemy of Trust", after Watts got arrested and defeated by Ironwood, the digraced scientist was first surprised when Salem and her army finally arrived to Atlas. But that surprise quickly turned into a sadistic glee, with Watts showing a content smile on his face; knowing what Atlas is about to get what's coming.
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.
In "A New Approach", when Watts secretly remotely communicates with Tyrian after they both arrived in Mantle, he reminds the concerned scorpion Faunus that finding a single hideout will draw suspicion and discovery from their enemies. Watts even reassures Tyrian that they will reaffirm their plan by staying mobile. He even mentions the security code in Mantle hadn't been updated unlike the cyber security code in Atlas, to which Tyrian agrees.
In "Out in the Open", Watts and Tyrian listen to Robyn Hill and Ironwood's announcement, informing the people of Mantle of the two criminal's activities, enraging Tyrian. Watts calms the serial killer down, having come up with a plan. He tells Tyrian to keep the people's attention in Mantle, causing the latter to prompt how Watts wants him to accomplish more panic than a Grimm invasion. Arthur rhetorically tells Tyrian if anyone in Remnant could deliver that, it would be him. This gives Tyrian the idea to attack Robyn Hill later in the night.
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 Atlas, 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 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 had little interaction, but when the news of Ozpin's return reaches Salem, Watts and Tyrian are ordered to deal with General Ironwood so he does not undermine their plans for Vacuo.
In Volume 7, it's revealed that Watts has an antagonistic professional history with Ironwood. He claimed that the General had played a role in getting him disgraced in the first place. Ironwood personally considered Watts "a pain in the ass" and likely took issue with Watts' arrogance regarding his intellect and scientific contributions to the military.
During the chaos in Mantle when Watts flies up to Amity Tower to sabotage, he only finds it unfinished. He is then locked inside the Colosseum and confronted by Ironwood, revealing Amity to also have been a trap. Watts hacks into the Colosseum and activates the Anti-Gravity biome before pulling out his revolver and proclaiming that he won't go down without a fight, showing that he is not afraid to go one and one against the Headmaster of Atlas Academy.
During their fight, Watts claims Ironwood never appreciated his genius, calling James out for standing atop his own intellect and using it to "call himself a giant". Ironwood disagrees, saying he had given Watts everything he could have wanted, to which Watts retaliates by saying that he chose Pietro over him. After Arthur is defeated, Ironwood tells him that he'd sacrifice everything to stop Salem. Watts spits at him, telling James that he hopes Ironwood does.
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". He would take any and every opportunity to insults and belittle the duo whenever he could. Seeing how he agreed with Raven Branwen's snide insults and remarks on how the two of them were only children being manipulated and tricked by Cinder into following her, much to the duo's contempt.
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.
Not much known to Watt's relationship to Jacques. But in "Pomp and Circumstance" it is shown when Watts made an unexpected visit in the Schnee Manor, Jacques is shocked to see him again, believing the disgraced scientist was dead. Watts dismissed the notion, claiming that was his intent the whole time.
Watts also seems to be aware of Jacques' issue with General Ironwood and makes a dubious offer in order to aid his Dust Company and for Jacques to win the election.
Though after Jacques gains the council seat, Watts shuts down the heating generators in Mantle using the newly given high access clearance afforded to Jacques as a councilman. Despite knowing full well that his deal with Jacques would be revealed and Jacques would then be held accountable for it, Watts had only considered Jacques as a pawn to further his and Salem's goals.
In "Pomp and Circumstance", there wasn't very much interactions shown between Watts and Whitley, except that Whitley seems to be a bit nervous and suspicious of the disgraced scientist's character. Watts complimented to the young boy that he resembles so very much of his father in a "creepily" way to add.
Councilman Sleet is a member of the Atlas Council and as such was once a close associate of Arthur due to him being one of Atlas' top scientists and researchers and seemed to have known him and worked alongside him during his days working for the kingdom, as seen where he was able to immediately identify Arthur during the events of "As Above, So Below".
Councilwoman Camilla is a member of the Atlas Council and as such was once a close associate of Arthur during his days working in Atlas as a scientist and researcher and was known to have worked alongside her during his days in the kingdom as seen when she was able to immediately identify him during the events of "As Above, So Below".
Before Watts had faked his own death and joined Salem, he used to work with a team consisting of Pietro and three unnamed scientists. During their time, other scientists thought Pietro's rivalry with Watts was overshadowed by their friendship, only to be proven to be wrong. After Watts faked his death, Pietro was supposedly shattered by the event.
In "Worst Case Scenario", Pietro is seen having kept an image of this team, where Watts is seen glaring at Polendina.
In "Gravity", it was revealed that Watts has restained relationship towards Pietro, being vengeful over him for being chosen by Ironwood over him and even going far as calling him a "fat imbecile" out of spite.