The vanilla WoW Horde leveling guide you see on this site was originally made back in 2006 by Joana (AKA Mancow, or FuriousPaul). The guides have been tweaked many times over the years to make things "faster". The leveling guides were made because of all the messages I got from people asking me how I was able to level up so quickly on new realms. I was first to level 60 on 7 different realms (3 with Mancow and 4 with Joana), even winning Blizzard's "First to Level 50" contest they held back in 2006.
Ion Hazzikostas: "... an engineer named Omar Gonzalez, who is on the Classic team, tried the method of taking the modern client, the modern server and teaching it to interpret the old 1.12 classic data. He kind of locked himself away for a few weeks, and came out with something that was a prototype--it was very rough, contained tons of bugs, the world wasn't fully rendered, but it was the original classic world, pre-Cataclysm. It had the original skills and talents, and we knew there's was a ton of work to do, but we felt like we realized for the first time, "we can do this." "