Dick Grayson debuted in the Golden Age of comic books as the companion to the Dark Knight himself. Over time, he'd become the ultimate sidekick before claiming his own identity by becoming Nightwing. Throughout it all, Dick remained hopeful and level-headed, thanks to his already wholesome attitude and his many mentors' wisdom.
Indeed, Dick would not be where he is today if it weren't for the people who encouraged and supported him, lifting him to heights he might have never reached otherwise. All of these teachers contributed to the making of Nightwing, showing him how to fight, but more importantly, how to be a true hero.
Superman
It wouldn't be an overstatement to say that Superman inspires nearly everyone in the DC universe in one way or another. In the comics, Superman turns evil more than any other member of the Justice League (except for Hal Jordan, of course), but he is the ultimate role model for the most part.
Still, Superman and Dick have one of the most intriguing relationships. Superman watched Dick grow and become his own hero. Now, he sees Nightwing as an equal, to the point where he asks Dick to mentor Jon Kent. For his part, Dick grew up looking up to Superman, and even if the Man of Steel never directly trained him, his influence is all over Dick's way of thinking.
Lady Shiva
The most dangerous woman in the world is often an ally of Nightwing and the Bat-Family. She also trained several of its members, most notably acting as one of Batman's best mentors after Bane broke his back.
In the New 52 continuity, Lady Shiva and Nightwing face each other, and she hints they have a history together. Dick mentions training under Shiva's tutelage in many iterations, adding even more layers to his background. Dick is one of the most gifted hand-to-hand combatants in DC, so it makes sense he learned from the best.
Raptor
Raptor is one of Nightwing's most notorious villains. The man who would become Raptor began as Richard, a circus performer who contracted Leprosy as a child. The illness left his body covered in callouses, rendering Richard immune to any physical pain.
Raptor acts as Nightwing's partner and mentor during the Better than Batman storyline. He is brutal, but succeeds in teaching Dick more about himself. The partnership ends in betrayal, but Dick still learns plenty from Raptor and comes out from the relationship with his faith strengthened.
Deathstroke
Deathstroke might be Dick Grayson's archnemesis, but he's also acted as a mentor of sorts over the years. The two share a complicated relationship that goes from outright hatred to something akin to respect. During the 80s, Deathstroke was the Teen Titans' Big Bad, turning his rivalry with Dick into a personal one. However, the years have been kind to this pair's dynamic.
During the Future State event, Slade Wilson becomes a mentor to Dick. It was a bold editorial decision that ended up working against all odds. Dick even becomes the new Deathstroke in DC's dark future. These two will never see eye to eye fully, but they can indeed work together and learn from each other.
The Haly's Circus Troupe
Every fan knows that Dick Grayson was part of The Flying Graysons alongside his parents. The team was the main attraction of Haly's Circus, and Dick found a family among the troupe, including his then best friends, Raya Vestri and Raymond McCreary.
Dick has fond memories of his time with the circus. He learned a lot from the troupe, particularly the importance of humility and compromise, even in the face of success. Dick also has a soft spot for Mr. Haly, the older man who ran the circus. Haly's troupe taught Dick that family could sometimes come from the most unexpected places, a lesson he would apply numerous times in the future.
John & Mary Grayson
Dick's parents, John and Mary, were gifted acrobats who taught their son everything they knew. Together, they made up the Flying Graysons team, becoming instant sensations with the crowds everywhere they went. John and Mary would ultimately die in an accident staged by mob boss Tony Zucco, setting the stage for Dick's arrival at Wayne Manor.
John and Mary were loving parents who taught Dick the core values he would cherish for the rest of his life. They also encouraged Dick's love for gymnastics and taught him the talent that would eventually transform him into the best acrobat in the world.
The Teen Titans
Dick Grayson served as a founding member and leader for the Teen Titans. He came into his own as a leader and hero with the team, stepping out from under Batman's shadow. He also adopted the Nightwing identity while with the team, confirming his maturity.
Despite being the team's leader, Dick also learned a lot from his fellow teammates. He practiced patience and understood the value of listening to others' opinions and inputs. This would go a long way in his efforts to differentiate and distance himself from the Dark Knight and contribute to Dick's cementing his heroic and hopeful persona.
Alfred Pennyworth
Dick has referred to Alfred Pennyworth as his father on multiple occasions (and on some others, he snarkily relates to the butler as his "mom"). He also thinks of Bruce as a father figure, but he has a special place in his heart for Alfred. The two have one of the best relationships in Batman comics, often forming a partnership to fight Bruce's worst and most stubborn impulses.
Acting as a warm and supportive parental figure means that Alfred was crucial in Dick's formative years. Furthermore, Alfred taught Dick the importance of listening to his instincts instead of blindingly following Batman. This, in turn, created the bright and optimistic persona that makes Dick stand out above all other DC heroes.
Batman
Bruce Wayne taught Dick Grayson everything he knew and then some. The Caped Crusader took Dick in and helped bring closure for the Grayson's murders, thus saving Dick from suffering Bruce Wayne's fate. Batman then taught Robin all the skills necessary to become a crime fighter, while Bruce taught Dick everything from languages to literature, encouraging his interest in forensics and computer science.
It's impossible to undermine Batman's influence in Dick's life. The Dark Knight is arguably the single most important person to Dick, and he one of the many reasons Nightwing is DC's most wholesome hero.