Steve is a human character originating from the world of Minecraft, and a major character in the earlier seasons of the SMG4 series, making his first major appearance in the episode "Super Mario 64 Bloopers: World of Craftmine" which is the first Minecraft-themed blooper made by SMG4.
He made many appearances in SMG4's videos, mostly in the 2014-released bloopers. He has still made occasional appearances after 2014.
In SMG4's bloopers, Steve is often seen derping around like crazy and prone to Creeper attacks in his own world of Minecraft. He likes humping things, like pigs and other animals. He also likes chicken and tends to chase them.
In the video "Super Mario 64 Bloopers: Super Mario Attorney", it is shown that you have to always ask him a very exact question, or else he will answer with a general answer. In "Mario VS Steve", he hates people who claim Minecraft is a bad game, to the point where he fought Mario.
Outside of SMG4's videos, he is the default skin for Minecraft players. In SMG4's bloopers, he made his first appearance in the video "Super Mario 64 Bloopers: World of Craftmine", derping out wildly when Mario plays a retro-instrumental version of one of Justin Bieber's songs and running into a pool of lava, and saying his first line, "PINGAS PINGAS PINGAS PINGAS PINGAS PI-" when Mario was going to blow up diamonds with TNT to attempt to get coal. In future bloopers, Steve is seen derping out often. In the episode "Super Minecraft 64 Bloopers: Mineswap", he switched body shapes with Mario, and in the blooper "Super Mario 64 Bloopers: Birthday Freakout.", Steve was one of the guests invited to Roprinplup14's first and second birthdays.
In Super Mario 64 Bloopers: Super Mario Attorney, he jugulated a Goomba and blamed it on SMG4. In this episode, he also shows that he can speak like any normal character, answering Mario's question with barely any difficulty. In the earliest Minecraft bloopers, Steve appeared to be partially mute, and only communicated through media clips. In SM64: ṩṩἔᾗмὄḋᾗᾄʀ 7 (TOAST edition), he became a superhero able to save the world: Captain Steve.
He also appears as a prince in the blooper "SM64 Guides: Toadsworth's How to - Princess". In "Super Mario 64 Bloopers: Spells n' Wiztards", he became a wizard, along with Mario, SMG4, Bowser, SuperMarioGlitchy3, and Po the red Teletubby. He once did a trip to the city in "SM64: ṩṩἔᾗмὄḋᾗᾄʀ 8 (150k special)". In "Sonic The Derphog: The Evilness Of Eggman(?)", he joined SuperMarioGlitchy3's club of bad guys to become evil. In "SM64: ṩṩἔᾗмὄḋᾗᾄʀ 10 (350k apocalypse special)", he was a candidate for some presidential elections, but it's unknown if he got elected at the end of the voting. He became a police officer in "SM64 Bloopers: Can the Villager come out to play?".
Steve has also started to play a supporting role in recent videos. For example, Steve was part of the group that fought Waluigi during the rap battle in SMG4: War Of The Fat Italians 2018 and helped stop the Minecraft Plague.
Steve is a human, cubic and pixelated like the other characters coming from Minecraft. His physical appearance scares some people, as seen in the episode "SM64: ṩṩἔᾗмὄḋᾗᾄʀ 8 (150k special)". His skin is rather normal, and he has brown hair and purple (and white) eyes. He usually wears a cyan T-shirt with short sleeves, blue trousers and gray shoes.
In a few episodes like "Super Mario 64 Bloopers: ṩṩἔᾗмὄḋᾗᾄʀ (1,000 Subs)", Steve's face is a bit different because an update to Minecraft changed Steve's mouth.
In a few old bloopers of SMG4, Steve wears a sort of T-shirt which has the same color as the trousers (dark blue) instead of his usual cyan T-shirt.
In some recent videos, he is sometimes seen almost naked, but wearing white underpants.
In some bloopers released in the year 2014, he has several alter-egos, like Captain Steve or Prince Steve for example (see below), then several alternate looks.
In the video "Super Minecraft 64 Bloopers: Mineswap", he and Mario accidentally swapped their body shapes, and then Steve has the same body shape than a lot of other guys in the bloopers, except his eyes and mouth hadn't really changed. He wore a cyan cap (same blue than the T-shirt (which had long sleeves instead of short sleeves)) and white gloves (he usually doesn't wear cap and gloves) and his shoes were of a very pale blue, nearly white, instead of gray.
In the blooper "Ssenmodnar 9 - Time Travel Edition", Steve was seen to have contracted Goomba herpes, a disease similar to Goomba diabeetus. It caused him to partially become a Goomba, making him look like a Goomba with a Steve head.