Rimuru Tempest

"It's simple. I want to create a world where life is as convenient as I wish it to be. A comfortable world where everyone can laugh and enjoy their lives as much as possible. That's what I truly and honestly want. Ideals without power are nonsense, and power without ideals is empty, right? I'm a greedy guy, but I don't have an interest in seeking power just for the sake of power, without the ambition to do something with it."

Rimuru Tempest (リムル゠テンペスト) is the main protagonist of That Time I Got Reincarnated as a Slime and the reincarnation of Satoru Mikami.

Slime
In his regular form, Rimuru takes the appearance of a usually spherical and sometimes amorphous mass of slightly blue and translucent ooze. Initially, Rimuru's slime form has a diameter of around 40cm, this increases to 70cm after his evolution to Demon Slime and further increases to between 80-100cm after his reincarnation to Ultimate Slime.

Human
Rimuru's facial features in human form are nearly identical to those of Shizu, but his long silver hair and deep golden eyes give him an otherworldly divine beauty that sets the two apart. He can occasionally be seen wearing Shizu's mask or donning dragon-like wings.

Initial
Rimuru's initial human form before consuming the orc disaster was that of a child that looked no older than six or seven. His hair was relatively short and he wore a simple outfit made of pelts before switching to his more iconic shirt, pants, and leather jacket combination.

Demon Lord Seed
After consuming the Orc Disaster Geld Rimuru gains another 10cm in height and significantly longer hair, making him appear as a child around the age of nine. His primary outfit in this time period consists of loose black pants and a white & gold shirt both woven from silk mixed with his own Steel Thread. Overtop this he wears a thick black (blue in the anime and manga) jacket and a fur scarf both made from the pelt of the Direwolf Boss.

True Demon Lord
After his harvest festival and evolution into a Demon Slime Rimuru gains another 10cm in height, making him appear as a child around the age of ten to twelve. During this period his primary outfit consisted of black pants, a black & gold shoulderless shirt, his fur scarf, and a black haori with white accents down the sleeves.

Ultimate Slime
After his "evolution" into a True Dragon and subsequent reincarnation into an Ultimate Slime, Rimuru's human form is that of an androgynous albeit girly 15-16 year-old adolescent. His main outfit consists of black pants and a black sleeveless long shirt accented with white boots and white stripes respectively. His arms have black detached long sleeves with golden ornaments at the top as well as a golden collar piece around his neck. His white rope-like belt has a metal loop at the back for the purpose of tying his swords scabbard. He can also occasionally be seen wearing a cloak over top of this outfit.

Additionally, Rimuru has been seen wearing a more casual version of this outfit with a more simple pair of overly baggy black pants and a white shirt in place of the originals.

Personality
Rimuru is an eccentric and childish person by nature but this shouldn't be mistaken for immaturity and naivety. Underneath the surface Rimuru is constantly analyzing, planning, and weighing the pros and cons of his actions, taking the smart move in the long-term over more rash and emotional decisions. In stark contrast to this normally composed and calculative demeanor, he's absolutely ruthless when it comes to handling people who have angered him. He'll go as far as brutal torture and murder without batting an eye if he can get away with it and uses more subtle methods like intimidation and blackmail when he can't.

Rimuru also takes a great deal of care with his personal image, lying on official accounts, erasing memories, and creating forged historical documents to make him come off as a more kind and benevolent person than he actually is in reality. Despite his often selfish and nefarious tendencies, Rimuru does deeply care for his subordinates, viewing them as something like a family or collection of children. And thanks to the memories of Satoru Mikami and Shizu Rimuru has access to a robust set of human ethics to rely on when his more cruel monster self isn't up to the task.

His goal in life is to create a convenient world where he can kick back and lazily enjoy entertainment similar in quality to what is found on Earth.

Trivia

 * Rimuru has a lot of knowledge about video games and manga.
 * Rimuru's unofficial birthday is February 20th 2013, as it was when the first chapter of the original web novel was released.
 * Rimuru has an aesthetic preference for Elves.