Oliver Queen has had several mentors on Arrow that turned him into one of the Arrowverse's best warriors. A big part of what makes Stephen Amell’s Oliver Queen such a formidable character is that he was mentored by multiple heroes and villains. Unlike several other Arrowverse superheroes, Oliver owes his skills to more than just one character. That’s largely due to the fact that Oliver didn’t stay in one place during the five years that he was missing.
The first five seasons of Arrow explored Oliver’s experiences while he was away. Originally, it was believed that Oliver was trapped on Lian Yu for all five years, but this was never the case. He went through a lot on the island, but it was only a part of his story. Sometime after leaving Lian Yu, Oliver spent a considerable amount of time in places like Hong Kong and Russia, and his adventures brought him into contact with a diverse group of characters who played integral roles in Oliver’s evolution into the Emerald Archer. Many, like Dr. Anthony Ivo (Dylan Neal), Kovar (Dolph Lundgren), and Baron Reiter (Jimmy Akingbola) were major antagonists in the flashback portions of the show.
Others, however, helped him on his journey; some were allies who imparted their knowledge and skills onto Oliver. Thanks to the training and guidance he received from them, Oliver was able to become a capable fighter and archer in the Arrowverse.
Yao Fei
In the Arrow season 1 flashbacks, Byron Mann’s Yao Fei became the first character to take Oliver under his wing. He’s also the reason why Oliver developed an interest in archery. He started training him shortly after their first meeting on Lian Yu. Having no real survival skills of his own, Oliver had to depend on help from Yao Fei, who instructed him in the use of a bow. Unfortunately, Oliver didn’t get to learn as much from him as he could have, as their time together was cut short by Yao Fei’s untimely death at the hands of Edward Fyers (Sebastian Dunn).
Deathstroke
Following Yao Fei’s death, Oliver paired up with Manu Bennett’s Deathstroke, who became his biggest ally in the season 1 and season 2 flashbacks. During this time, Slade Wilson taught Oliver how to fight with more than just an arrow. As a highly-disciplined mercenary with years of experience, Slade was a great teacher for Oliver, who at first struggled to match Slade’s expectations for their training sessions. From Slade, Oliver learned how to fight with several different weapons, including staves and swords. He also picked up a number of martial arts styles, which he ended up incorporating into his fighting style.
Shado
When Shado (Celina Jane) began accompanying Oliver and Slade, she decided to take over Oliver’s training. She picked up where her father left off by teaching him archery, and also helped Oliver improve his physical capabilities with exercises that enhanced his strength and reflexes. After Shado’s death, Oliver took her green hood - which had also belonged to Yao Fei - and wore it to honor both of his mentors.
Maseo & Tatsu Yamashiro
After Oliver was forced to work for Amanda Waller (Cynthia Addai-Robinson), Maseo Yamashiro (Karl Yune) was assigned to be his handler. Under orders from Waller, Maseo trained with Oliver and took him out into the field with him. While living with Maseo and his family, Oliver found out that Maseo’s wife, Tatsu (Rila Fukushima), hated him. But over time, she warmed to Oliver and ended up giving him guidance. She also taught him a meditation technique that he continued to use long after returning to Star City. In the present-day story, Tatsu returned as an ally, while Maseo became a villain and a member of the League of Assassins.
Anatoly Knyazev
During his stay in Russia, Oliver spent a great deal of time with his good friend, Anatoly Kynazev (David Nykl), who helped Oliver adjust to being involved in organized crime. During the Arrow season 5 flashbacks, Antaloy was a voice of reason for Oliver, who often looked to him for advice and help. The strength of their brotherly bond was demonstrated in other stories, and though it was tested by a brief villainous turn for Anatoly, the two were able to remain friends. Anatoly even served as Oliver's spy in Diaz's crime ring in season 6. The character paid his respects to Oliver by attending his funeral in the Arrow series finale.
Talia al Ghul
Arrow season 5 revealed that Yao Fei, Deathstroke, and Shado weren’t the only people responsible for making Oliver a deadly martial artist and archer. One of his most important teachers in the Arrowverse was Talia al Ghul (Lexa Doig), the woman who trained Yao Fei and the daughter of Ra’s al Ghul (Matt Nable). After tracking down Oliver and learning of his plans to eliminate the people on his father’s list, Talia taught him the skills of the League of Assassins, and helped transform him into a force to be reckoned with.
When his training with Talia was complete, Oliver was given a new green costume and bow - at that moment, the Hood was born. Years later, Talia came back into Oliver's life to seek revenge for her father, but in season 7, she was utilized as an ally. In fact, she eventually co-founded the League of Heroes with Thea (Willa Holland). Along with Anatoly, Talia was one of two of the Emerald Archer's mentors to make an appearance at his funeral.
Ra’s al Ghul
Most of the training Oliver received in the Arrowverse came before Arrow season 1, with one exception being the show’s League of Assassins story in season 3. After being forced to accept Ra’s al Ghul’s offer for him to become the Heir to the Demon, the Assassins began grooming him to take over their master’s position. As an Assassin, Oliver received an all-new look and was personally trained by Ra’s al Ghul himself. Through him, Oliver became an even better warrior.
Despite everything that Oliver had learned from his previous mentors, all of their experiences paled in comparison to Ra’s al Ghul’s, especially since he had been around for centuries. Thanks to him, Oliver sharpened his skills as a swordsman and learned new fighting styles. Of course, he still wasn’t good enough to beat the Demon in a fair fight in the Arrow season 3 finale, but in the end Oliver did succeed in killing him and granting Ra’s’ wish to die at Oliver’s hand.