I'm not sure why that's the relevant part, but the part of the Obama administration responsible was CIA director Brennan, who was doing similar stuff during the G.W. Bush administration and just happened to give it an official name while Obama was around.

It's nowhere near the first kill list the US has had, it's just the first one called "Disposition Matrix". Previous administrations had other names. For example: https://en.m.wikipedia.org/wiki/Executive_actions_of_the_CIA