Simon Thomley

From Sega Retro

Simon Alexander Thomley
Place of birth: United States
Date of birth: 1979-08-11 (age 44)
Employment history:
Role(s): Programmer[1][2]
Forum user name: Stealth
Twitter: @HCStealth

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Simon "Stealth" Alexander Thomley is an American programmer and video game developer[1], and founder of game development company Headcannon[2], known for being one of the earliest key members of the Sonic scene.


Thomley is noted for creating multiple Sonic the Hedgehog-series game modification utilities, such as SonED, and is also responsible for producing one of the first Sonic games made in C++ - Project Mettrix. Thomley was also one of the first individuals whose fansite, the now-defunct Organized Chaos, was incorporated into the Sonic Stuff Research Group.

In his later work with the Sonic scene, Thomley became famous for being the first coder to fully implement the character Knuckles in the original Sonic the Hedgehog as Knuckles the Echidna in Sonic the Hedgehog. In addition, he has contributed a significant amount of work toward the development of the famous romhack Sonic Megamix, and is one of the founding members of Team Megamix.


Main article: Headcannon.

In November 2012, Thomley founded independent video game development company Headcannon in preparation of working with Christian Whitehead on the Android and iOS ports of Sonic the Hedgehog and Sonic the Hedgehog 2. A corresponding website was launched on March 9, 2013 (three weeks before the port of the first game was revealed at GDC 2013), and each of the company's projects was subsequently given a dedicated section on its release. Thomley continues to operate and credit himself under the Headcannon name for his development projects.

Prior to the official development of Sonic the Hedgehog CD (2011), Thomley had assisted Christian Whitehead in creating a pitch demo of the title by providing information gained and pseudo-code developed from reverse-engineering certain original Sonic gameplay elements such as Sonic the Hedgehog CD's Special Stage, and the boss mechanics of EGG-HVC-001. This work was done before Headcannon had been established, and once development had officially started, Stealth would not develop for the series again until Sonic the Hedgehog (2013). Nevertheless, he received credit in the game's "Special Thanks" section, and as with other entries he developed for, he is credited by his full name of Simon Thomley.

Thomley also produced the Headcannon Game Engine, a script-based multi-platform 2D game engine with corresponding development tools.

Sonic scene

Throughout the years, Thomley has also taken on important or otherwise respectable roles in the Sonic scene.


Production history

  • (; 2011) — Special Thanks
  • (; 2013) — Programmer
  • (; 2013) — Programmer
  • (; 2017) — Programmer (as Simon "Stealth" Thomley)
  • (; 2017) — Programmer (as Simon "Stealth" Thomley)
  • (; 2017) — Programmer (as Simon "Stealth" Thomley)
  • (; 2022) — HEADCANNON Lead Developer + Lead Programmer
  • (; 2022) — HEADCANNON Lead Developer + Lead Programmer
  • (; 2022) — HEADCANNON Lead Developer + Lead Programmer
  • (; 2022) — HEADCANNON Lead Developer + Lead Programmer


Main article: Photos of Simon Thomley

External links