Path to Glory
Way, way, way back in the dawn of Warhammer Fantasy Battle and Warhammer 40,000, Games Workshop released two books that covered the forces of Chaos for both settings. These were Realms of Chaos: Slaves to Darkness (Khorne and Slaanesh) and The Lost And The Damned (Nurgle and Tzeentch). As part of their rules these books contained "Path to Glory", a mini-game that blurred the lines between wargame and roleplaying game that allowed players to take the roles of Chaos Chosen, Aspiring Champions who would fight (mostly each other, but also, potentially, other races and monsters) to try and attract the favor of the Dark Gods, with the game ending with death, damnation or daemonhood.
Fast forward many editions...
Do you remember when White Dwarf was awesome? Because, after the first half of the release of Hordes of Chaos, White Dwarf spent the first four months focusing on god-related fluff and model articles... and then the next five months on updating Path to Glory to 6th's rules. And when Beasts of Chaos came out, they did a special update article, allowing for beastman aspiring champions in Path to Glory as well.
Sadly, with 8e and White Dwarf's descent into suck, Path to Glory has been left behind, languishing in the darkness with all the other awesome things of those days.
Now however revamped versions, of "Path To Glory" have been rereleased for both AoS and 40kK as a digital download during the Black Library advent calendar thing.
Tactics For 40K are here.
Tactics for Age of Sigmar are here.
Path to Glory 6e Articles
White Dwarf 275 November
The daddy of Path to Glory 6e, this article had the basic rules for founding a warband to play the game with, including tables for determining followers and equipment. Perhaps coincidentally, this issue also had the preview list for Beasts of Chaos, to provide stats and rules for the followers associated with that army.
White Dwarf 276 December
Rules for gaining favor points and for Advancements - the ability for the warband's Champion to score increases and abilities depending on luck and the whim of the Dark Gods. Simpler than the originals back in Realms of Chaos in that only the Champion advances and evolves, with followers remaining vanilla. It also included the basic rules for handling injuries and what happens if your Champion turns into a Chaos Spawn as a result of a bad Power Advancement roll or due to acquiring 5 Mutations.
White Dwarf 277 January
A simpler article, this one includes a set of six scenarios to play when fighting on the Path to Glory.
White Dwarf 278 February
Expanded mutation tables, replacing those from the original table back in 275 with god-specific ones, from Tzeentchians able to swallow opponents whole to Nurglites with xenomorph-style jaws to Slaaneshi with snake-like bodies to Khornates who absorb enemy spells to get stronger. It also includes more detailed rules for handling what happens to a Champion, or even a follower, who gets taken out in one battle.
White Dwarf 279 March
Rules for a multi-warband battle scenario and some magical items to receive as a result.
White Dwarf 284 August
Coinciding with the official release of Beasts of Chaos, this issue's article focuses on Beastman Aspiring Champions and the unique warbands they gather.
Black Library Advent Calendar December 2015
Neckbeards may rejoice knowing that Geedubs have brought back "Path to Glory" has been brought back for both Age of Sigmar an Warhammer 40K. Allowing you to create your own warbands oncemore.
The Age of Sigmar General's Handbook includes an expanded version of the Path to Glory released by Black Library last december, differing from usual because it also allows to non-chaotic armies to be used, adding tables for Stormcast Eternals, Skaven, Fyreslayers, Ironjawz, Sylvaneth and Death armies.