Alan Shutko
Explorer
The "kill stuff for points" idea is common to many videogames, but it started with D&D.
Actually, I think it started with people who house rules away "gold for XP". There were always more than one route to XP, but most people house ruled parts away.
I think goal XP was officially endorsed as of 1989 (AD&D 2e) and I think earlier in modules. But what's 23 years among friends?