One of Nero's most defining traits is his utter love for adventure. Whenever his crew stumbles upon a new island, he is the first (and sometimes the only) one that wants to explore the area. Even when hearing noises from incredibly large animals, he still wants to venture the area and see what he can find.
Though he is far from stupid, Nero can be gullible and oblivious to what should be obvious. For example, he fell for Kairi's attempt at passing for a man, to which Shino says that Nero "could fall for anything". However, he doesn't let his enemies fool him as easily. An example would be when he didn't fall for Hakan's attempt to play on Nero's sympathetic side, which was far more convincing. He can also be quick to anger, and is quite childish at times. He is also quite impulsive, as he tends to jump into things without thinking them through beforehand.
Another trait Nero has is utter lack of care for authority. In the face of royalty, powerful pirates, elders, or young people, Nero will talk to them all the same. Nero views all people as equal to each other and doesn't believe in rank or hierarchy. Even among his crew. Despite being the captain, he doesn't force them to call him captain or boss them around or make them fear him. As he feels like if they respect him without fearing him, they will be completely loyal to him. In fact, the only time Nero will pull rank on his crew is when he wants to go adventuring and they don't want to, he will say "I'm the captain, so I decide where we go".
Nero possesses a rather strong competitive streak, as Tristan says "Whenever there's a contest, you're always ready' to go". Nero has a lot of self-confidence and possesses a large ego to match it, making him sassy, cocky, quick-witted and sometimes overconfident in his abilities. He has a lot of attitude, shows a lot of sarcasm through his gestures and has a narcissistic tongue. He often jokes around to light the mood, but will also take any opportunity to taunt and mock his opponents, and takes many of the dangerous situations he faces lighthearted. He is also not generally modest when it comes to his abilities and is very proud of his skills, smug and a showoff. However, Nero can admit when he is being outdone and he can admit to his own flaws and mistakes. Such as after the time-skip, he apologizes to his crew for not being as strong as he should've been and this time he will protect them at all costs.
Nero is also not generally disturbed by battles or bloodshed, as he has been fighting his entire life. During the Whitebeard War, he understood that everyone here cannot be saved and people are going to die. In fact, Nero loves a good fight and is always ready to brawl with the toughest opponents. The only time he is disturbed by bloodshed is when it involves his friends, or a horrible act such as slavery.
Despite caring for his friends and their dreams, Nero is actually pretty selfish. When it comes to his adventures and finding the One Piece, his crews opinion doesn't matter to him. When he is dead-set on something, he can't be swayed away from it. Such as when Kyla said they shouldn't go to Kuro Mountain, but Nero said it looked like a fun place to go. He will however, take what his crew thinks into account and often times will even let them make certain decisions for him as he treats them as equals rather than subordinates.
Nero's alignment can be described as "Chaotic Neutral". He is an individualist who follows his own heart and generally shirks rules and traditions. Although he promotes the ideals of freedom, it is himself and his crews own freedom that comes first; good and evil come second to their need to be free. Nero has even said before that he is not a hero, he's a pirate. He doesn't actually believe in good or evil in a general way. He even says that he "doesn't care about the good or the bad" His morality is extremely subjective, almost twisted: while he values life in general, he expressed no resentment towards killers like Shino and Eustass Kid.
Nero also possesses an indomitable force of will; in situations where most others would give up and resign themselves to defeat or imprisonment, and in situations where he is severely outnumbered and outgunned, he always forges on, never loses faith in himself and never quits or submits. Nero is extremely loyal to his crew and other friends. He will fearlessly risk his life and even halt his adventure for them if they are in danger.
Like many One Piece characters; Nero has his own unique laugh, which is "Shihahaha"
Because he is the Captain and recruited all the crew mates personally, Nero cares tremendously for his crew. As far as captaincy is concerned, Nero sees his crew mates as equals, rather then subordinates (his crew mostly calls him by name, rather than with an honorific or "Captain"). Nero only pulls rank when he wants to go "adventuring", despite what his crew thinks.
Nero is the kind of benevolent pirate captain who does not seek to actively harm others unless they give him and his crew (or anyone he cares about) a very good reason to. However, while in Alabasta, he was willing to start a fight with Luffy over accidentally crashing into their ship. As the Sky Demon Captain, Nero was an unwavering faith in his crew. In fact, after the timeskip, Nero's trust grew even more as shown when he overheard that his crew were being arrested by an army of Marines, he did not seem upset at all, saying "They can handle it".
Because of this, while often annoyed by his impulsive nature, his crew trust him unconditionally. They also show great concern for him when he is put in life-threatening situations. It can be said that Nero has both greatly impacted and changed the lives of each of his crew members and is typically the one cited as having revived each of their dreams.
The fist member to join the crew Shino,