Toad's Bald! (A Super Mario Bros. Comic Dub)

His Personality:

Luigi is portrayed as timid and a bit of a coward. He is also extremely worrisome and is considerably self-conscious. However, he overcomes his fears and acts like a hero when necessary, such as when someone he knows is in danger or needs help. On the New Super Mario Bros. Wii website, it describes Luigi as "Mario's fearless brother". In keeping with his personality-based Power Flower, a sign in Big Boo's Haunt in Super Mario 64 DS describes Luigi as "wispy."

Luigi cowering at the sight of Boo Mario in Super Mario Galaxy

Arguably, Luigi's most apparent trait is his seeming cowardice. Though he showed several instances of cowardice in early non-game media such as The Super Mario Bros. Super Show!, his cowardly nature was not actually shown in-game until Luigi's Mansion (aside from a few hints in Paper Mario), and has carried over to almost all of Luigi's subsequent appearances. Although Luigi's phasmophobia is his most overbearing fear, he usually reconsiders at the mere thought of any monsters or trials, especially in the Mario & Luigi series. However, Luigi can be quite brave, and has saved the Mushroom Kingdom alongside his brother multiple times. Super Paper Mario especially glimpses into Luigi's more courageous side, showing him boldly rushing into dangerous situations and rarely even implicating his infamous cowardice. In addition, the endings for Luigi's Mansion: Dark Moon and Luigi's Mansion 3 also hinted that he overcame his phasmophobia, or at the very least takes exception to Polterpups and makes friends with the friendly ghosts of Evershade Valley and the Last Resort hotel. In Simon Belmont's reveal trailer for Super Smash Bros. Ultimate, Luigi is clearly scared of all the creatures in Dracula's Castle, though he attempts to ward them off with the Poltergust's flashlight, as well as a toilet plunger.

Another strong element of Luigi's personality is his apparent complex of being overlooked. Although his Superstar status has earned him many fans, including an entire fan club led by Toadia and multiple supporting Toads (one of which claims to be his biggest fan in Super Mario 64 DS), even Bowser and the Koopa Troop have occasional trouble with remembering his name (as seen in Mario & Luigi: Superstar Saga), and he appears to be almost unknown in the Beanbean Kingdom. Although Luigi's biggest reactions to his frequent overlookings in the Mario & Luigi series are a few "…"s and face-faults, his inattention was played up for comic relief in Paper Mario, with the snarky man in green complaining about being left behind and perpetually training for that elusive next adventure. Luigi's bio in Mario Party 5 states that he has been gaining popularity in recent years.

Luigi's state of being in the shadow of his brother shows strongly in Super Smash Bros. Brawl. An example would be the way Luigi is almost never happy, how his commentary is very monotoned, and how one of his taunts is a bashful kick of the ground. Also, his Final Smash, Negative Zone, seemed to have developed because of living in his brother's shadow forever. Additionally, whenever the crowd cheers for Luigi, not too many people are heard cheering for him and when the announcer says Luigi's name, he sounds a little surprised. Snake's codec conversation even has the Colonel refer to Luigi as the "kid brother" and "king of second bananas", despite Snake's protests. Despite this, however, Masahiro Sakurai did not intend to play up Luigi's overshadowed status, instead aiming to make him "everyone's favorite man in green."[21] Luigi's state in the shadow of Mario is present in other Super Smash Bros. games, since the original Super Smash Bros. addresses him as the "eternal understudy" when he's unlocked; Super Smash Bros. Melee also refers to him in a similar manner, and his cinematic in the game's Adventure Mode shows him Footstool Jumping Mario, signifying his tiredness of being number two. In Super Smash Bros. for Wii U, whenever a Palutena's Guidance conversation is activated when fighting against Luigi, Viridi and Palutena are quick to point out Luigi's status as "number two" in relativity to Mario, even though Pit held him in a higher regard.

LINE sticker showing Luigi's unhappier side.

The Super Smash Bros. games make Luigi a comical, yet depressive figure, which is evident by his aforementioned unhappiness, his violent taunt, quiet commentary, and origin of Negative Zone, yet, several other actions show Luigi behaving childishly. These include: his dash attack, where he swings his arms aimlessly while keeping a humorous panicking expression; his neutral attack, where he hits opponents with his butt for the third hit; his up tilt, where he "paw swipes" the opponent with his fists while closing his eyes; the aftermath of his Super Jump Punch, where he falls upside-down; his idle poses, where he scratches the back of his head sheepishly or humorously pulls his nose before wincing in pain; and his victory poses, which have him do the following: breathing heavily with his eyes half-closed, falling stiff and planking on the ground (also one of his taunts), or childishly making finger pistols and pretending to shoot his opponents (which is supported by him saying "Bang, bang!").

When Luigi finally went on a quest of his own in Paper Mario: The Thousand-Year Door, he's presented as more arrogant and somewhat of a liar, as he changes the stories of his adventure to make himself look better; his partners claim his stories are false. The novelizations of his escapades describe them with even more flowery exaggerations, stating for instance that he played an earth spirit in the Jazzafrazz Town Drama Slam (whereas he actually played grass on the side of the road, according to Hayzee) and that he awoke Cranberry with "a soft call" (rather than a sneeze).

In Mario & Luigi: Partners in Time, the Star Temple gate (which supposedly knows all) passes Luigi as "unworthy" to enter. This most likely has something to do with Luigi's "dark secret from his past," which it also mentions; Luigi did something either embarrassing or foolish which he has kept a secret ever since. However, in an interview with a member of staff, he stated that Luigi had no dark secret, and it was actually a reference to Luigi's constantly living in the shadow of his brother.[citation needed] Even the game itself makes a straightforward point that Luigi has a large heart, as proven when he hits the Aurora Block and it grows to a gigantic size, flattening him.

In Mario Strikers Charged and Mario Kart Wii, Luigi is shown to cry when he is frustrated and losing a game.

Luigi is also portrayed as somewhat refined, leading the "Luigi Gentlemen" in Mario Superstar Baseball. Luigi's Mansion shows him to be a bit of a neat freak, constantly criticizing the dustiness of his mansion and even mentioning at one point that he hand washes his cap as opposed to using a washing machine as his brother does. He also seems to have an eye for art, but does not appreciate many of King Boo's decorations. Luigi has also been known to cross-dress several times, usually as Princess Peach in order to trick their enemies. Luigi can be sensitive when someone insults him, especially if the jab in question regards his mustache (as proven prior to his showdown with Dimentio). Luigi also appears to show concern for cruelty to animals; he is horrified by the deer heads and leopard skin rugs in the Safari Room in Luigi's Mansion and declares that he will not stand for an animal being treated in such a manner.

In The Super Mario Bros. Super Show!, Luigi is consistently portrayed as being the smarter of the Mario Bros., but the cowardice trait is also shown as Luigi is scared of things going wrong. He also does not take as many risks as Mario does.

Revealed in Mario & Luigi: Dream Team is that he is willing to help his brother whenever he is in danger. He thinks that Mario is much cooler than he is, that he adores his brother because of this trait. The messages that appear in Dream's Deep further explains this trait.

He is also shown at times to be clumsy, as evidenced in the ending of New Super Mario Bros. Wii, where he accidentally locked himself out of the hot air balloon that Peach and Mario were on while waving goodbye to the Toads, and also ended up collapsing while trying to enter the hot air balloon, due to it having flown off.

Overall, Luigi's personality is hard to determine and changes depending on appearance. Very few games have portrayed him with a personality that lasts throughout the subsequent release. Overall, however, Luigi can be described as timid and cautious, yet kindhearted, brave, and willing to protect his homeland with Mario's help, though can have his flaws at times.

Ref: https://www.youtube.com/watch?v=J-gWGTHvcH8