Short answers, pulled from the story.
Masahiro Ito, the monster designer for Silent Hill 2, created Pyramid Head. He wanted "a monster with a hidden face" and arrived at the pyramid-shaped helmet after becoming dissatisfied with earlier designs that looked like humans wearing masks.
Pyramid Head represents James Sunderland's guilt and wish to be punished for killing his wife Mary. He functions as an executioner who pursues Maria, a delusion resembling Mary, forcing James to repeatedly experience guilt over her death.
Masahiro Ito, a German World War II tank enthusiast, drew on the lower hull of the King Tiger heavy tank when designing the edges of Pyramid Head's helmet. Other military vehicles from the same region and era informed additional design elements.
Roberto Campanella portrayed Pyramid Head, credited as "Red Pyramid", in the 2006 film Silent Hill and reprised the role in the 2012 sequel Silent Hill: Revelation. His costume took between two-and-a-half and three hours to apply, and his boots contained a hidden 15-inch sole that brought him just under seven feet tall.
Pyramid Head has appeared in the 2008 Nintendo DS game New International Track & Field, the 2017 game Super Bomberman R as "Pyramid Bomber", and as a purchasable killer called "The Executioner" in Dead by Daylight, added on the 16th of June 2020 via the CHAPTER 16: Silent Hill DLC. He also makes a cameo in the PlayStation 5 game Astro's Playroom.
Ito designed Pyramid Head specifically for James Sunderland's story in Silent Hill 2. He stated that other creators "really misunderstood Pyramid Head" and said that if he made another Silent Hill game, he would either exclude the character entirely or kill him off in the opening scene.