Appearance
His arms can apparently extend indefinitely, so it allows him to access the upper cabinets of his workplace without having to leave his original position. Kamaji appears to spend most of his time at his workplace, as he is seen sleeping and eating his meals there.
A number of Susuwatari (ススワタリ) work for him by carrying coal into his furnace. He has large cabinets where he keeps all the herbs that are used in the baths, which he crushes with a Yagen.
History
After some persuasion, he allows Chihiro to work at the bathhouse and even pretends to be her grandfather when questioned by Lin, to protect her, though this ruse does not stand for long. The next morning, he awakes to find Chihiro asleep in the boiler room after her meeting with Haku. He says nothing and simply places a purple pillow on her sleeping form.
He later takes Haku, heavily injured into his boiler room and cares for him while Chihiro, given train tickets by Kamajii, journeys to Zeniba's cottage. At first he, seems cold and uncaring, but by the end of the film, he seems to have grown a soft spot for Chihiro and for anyone whom she calls her friend.
Trivia
Kamaji is very similar in appearance to Dr. Eggman, the main antagonist from Sonic the Hedgehog, though there is no definite connection between the two.
His age is at least over 40, since he stated that he had been saving a railroad ticket for 40 years.
His appearance appears to be based on that of a spider, as evidenced by his 8 limbs and unique facial features. His mustache seems to represent the mandibles of a spider, and his goggles resemble a spider's eyes.