Marvel's Illuminati group has grown in size since I first encountered it, and apparently has been involved in many more of the Marvel universe's major incidents. I first became aware of them in Planet Hulk.
Which are the key issues dealing with the formation and actions of this group, and what's the best order to read them in? I'm wondering about issue before the dedicated Illuminati series that started in 2015.
Wikipedia lists their appearances by comic line, but isn't helpful in determining how those appearances actually influenced other stories, or determining a cross-series timeline.
