|“||My dad always said... "if you need to know a city, ask the rats."||„|
|~ Mercury Black|
|“||Let's just keep this between us friends.||„|
|~ Mercury, to Ruby as she fails to call for help.|
In the English dub, he was voiced in Volume 2 by J.J. Castillo and is currently voiced by Yuri Lowenthal, who also voiced Sasuke Uchiha and That Man. In the Japanese dub, he is voiced by Hikaru Midorikawa, who also voiced Vidaldus Taka and Baldren Gassenral.
Mercury lived in the mountains with his father, Marcus Black, who was an assassin and heavy drinker that would abuse and beat him. One night, he fought against his father and killed him.
Cinder Fall and Emerald Sustrai saw their fight from afar and were hoping to recruit his father for their cause. However, due to Marcus' death, Cinder asked Mercury if he took after his father. He joined Cinder's faction and has been traveling with them since.
In "Best Day Ever", Mercury and Emerald arrive at a book store owned by Tukson and Emerald asks him if he has certain books. Meanwhile, Mercury continues to pick up books and slams them loudly during Emerald's questioning before asking if he has any comics. When Emerald begins to reveal why they are really there, Mercury dims the windows of the shop and kills Tukson when he tries to attack them.
Mercury returns to Roman Torchwick's hideout with Emerald and informs Roman that they were out "cleaning up his problems". Cinder soon arrives and Mercury confirms that they had indeed killed Tukson before he had the chance to flee. When Roman tries to explain to Cinder why he hadn't done the job himself yet because of how busy he is stealing Dust, Mercury compares him to any punk with a gun and ski mask. He then leaves the warehouse with Cinder and Emerald.
In "Welcome to Beacon", Mercury arrives at Beacon with Emerald and Cinder, posing as students from Haven Academy. The three bump into Ruby Rose, where Mercury informs her that they got turned around looking for their building. Ruby then tells them the direction of their building and the trio continue on their way as Ruby welcomes them to Beacon Academy.
In "Extracurricular", Mercury is seen watching Pyrrha Nikos fight with Team CRDL in a class based training fight. Once Pyrrha finishes with the former, Mercury challenges her to a sparring match. Glynda Goodwitch briefly protests this, but Pyrrha gives her approval and the match begins.
The fight is tense, with both parties probing for weaknesses and studying their opponent's skills. Pyrrha briefly uses her Semblance of polarity to manipulate Mercury's boots, throwing him off-balance. Midway through the brief but intense match, Mercury abruptly forfeits, stating that Pyrrha, a world-renowned fighter, is completely out of his league. After the match, he briefly converses with Emerald and enthuses about how much fun he finds learning. He is later seen discussing Pyrrha's Semblance and skills with Emerald and Cinder in their dorm rooms, conveying his findings from their match.
In "Burning the Candle", Mercury enters the ballroom with Emerald and is welcomed by Yang Xiao Long, followed by his answer that both of them wouldn't miss the dance for the world.
In "Dance Dance Infiltration", Mercury is seen dancing with Emerald, while talking to Cinder through a headpiece at certain points throughout the dance. After Cinder arrives at the dance, having successfully completed her mission, Mercury dances with her and asks how her night was, to which she responds that it was much more exciting than expected.
In "Breach", Mercury appears alongside Emerald and Cinder during the Grimm attack on Vale, who silently nods to the two to attack and help in taking out the Grimm attacking humans. Shortly after the fight, Mercury, Emerald and Cinder are overlooking the city of Vale from a rooftop. When Cinder remarks on the day being successful, Mercury adds that with them having lost so much Faunus in the caves, the White Fang won't listen to them anymore. At that moment, Adam Taurus appears and reassures them that they will listen to him.
In "Round One", Mercury is first seen observing different boots at a stand in the fairgrounds. After Emerald is done conversing with Team RWBY, she returns to Mercury, and he asks if she got the information. She tells him Weiss and Yang will be fighting in the second round. He is later seen eating a big bowl of popcorn while spectating the match between Team JNPR and Team BRNZ along with Emerald and Cinder.
In "It's Brawl in the Family", Mercury witnesses the fight between Qrow Branwen and Winter Schnee. As soon as he recognizes Qrow, he becomes worried and runs off to report to Cinder.
In "Lessons Learned", Mercury and Emerald are faced off with Coco Adel and Yatsuhashi Daichi of Team CFVY in the double match due to Cinder rigging the match up. He and Emerald easily win the match.
In "Never Miss a Beat", Mercury is later seen doing push-ups in the Beacon dorms with Emerald and Cinder nearby as the latter looks through James Ironwood's files and finds information on Penny Polendina.
In "Fall", Mercury is elected to represent his faction in the finals round of the tournament, facing off against Yang in the first match. While the two are appear to be evenly matched in the beginning, Mercury unleashed a storm of rounds at her. Just as he walks away, brushing his clothes off in confidence of his "victory", Yang rebounds from his attack and proceeds to unleash a beatdown that costs him the match.
However, he is involved in an elaborate ruse where Yang is tricked by Emerald into seeing Mercury attack her despite his lack of Aura. This causes Yang to attack him in self-defense and "fracture" his leg; allowing him to frame Yang for seemingly assaulting a non-combative opponent. Emerald rushes to his side as he clutches his leg and cries out in pain. However, his legs are prosthetic, unbeknownst to the others present, and he can repair them himself.
In "Beginning of the End", Mercury is evacuated by Cinder and Neopolitan in an Air Bus to their secret warehouse where he hides away so that nobody knows his leg is fine. Cinder's plan carries on with him in hiding.
In "Destiny", Ruby finds Mercury in the stadium with fully healed legs. He notes that the next matchup, Pyrrha versus Penny, will be chaotic due to Pyrrha's polarity and Penny's metal body. Mercury then assumes a fighting stance, preparing to attack an unarmed Ruby.
In "PvP", Ruby attempts to both speed past Mercury and call for help via her Scroll, to no avail, as Mercury impedes her movement, and shoots her device from her hand. Ruby eventually manages to evade and escape, but only arrives to see Penny's destruction at the hands of her opponent. Seeing the plan was successful, Mercury leaves Ruby to grieve without further harming her, going back the way he came.
In "Battle of Beacon", Mercury is seen with Cinder and Emerald, standing on a rooftop as he is filming the Grimm's attack on Beacon with a Scroll. Cinder instructs him to focus on the infected Atlesian Knight-200s, before he is interrupted by the Grimm Dragon's arrival, which Mercury also focuses on.
In "Of Runaways and Stowaways", Mercury and Emerald watch Cinder receive "treatment" from Salem. Both he and Emerald back away in fear as a Seer comes in to report the Grimm's lack of success in finding the relic at Beacon Academy.
In "No Safe Haven", Mercury is seen watching Cinder train with Grimm and then incinerate a vision of Ruby created by Emerald.
Mercury also appears in the non-canon comedy spinoff series. Here, he is an outright villain helping Cinder.
In "Episode 18", he is seen with a gun that he calls "The Kitten Killer 9000." He then realizes that Cinder and Emerald are trying to hide the fact that they are evil from Ruby and Nora and leaves. The heroes remain oblivious to the trio's villainy.
In "Episode 19", he makes a brief appearance after being defeated in an evil scheme by Zwei.
In "Episode 21", he is seen trying to hide evil plans and equipment from Sun and Neptune. Later, in a fantasy where world piece is achieved, Mercury, as well as the other villains, are extremely distraught.
In "Episode 22", he is seen trying to get through airport security, but is constantly detected and stopped due to his metal legs as Emerald and Cinder, embarrassed, look on.
In "Episode 24", it is revealed that RWBY Chibi was "filmed before a live audience". Mercury and the other villains appear at the end for the curtain call.
Mercury is very carefree and enthusiastic, as he makes an effort to opt for excitement and action. He has a strategic mind shown during his match against Coco Adel and Yatsuhashi Daichi, where he takes advantage to hide before lauching a surprise attack on Coco. He also uses the geyser biome to his advantage, using it to create an opening on Yatsuhashi and defeat him.
Judging from the nonchalant way he talks, Mercury appears to have no qualms about killing, even speaks in an extremely derogatory and acrimonious fashion about Tukson murdered in cold blood.
- Mercury alludes to the Roman god Mercury, whose Greek equivalent is Hermes.
- Mercury's symbol, a winged boot, as well as his weapons, may be an allusion to the winged sandals of the mythological Mercury.
- His colors are black, gray, and silver, likely to give off the tones of the element mercury.
- Both Mercury and Emerald lacked 3D models in Volume One, using 2D still image sprites instead.
- Mercury's last name, Black, was originally suggested by his previous voice actor J.J. Castillo.
- Mercury's appearance, his facial features in particular, is similar to that of Sasuke Uchiha. They also share the same English dub voice actor, Yuri Lowenthal.