This is what happens when you go to conventions. You wander all around, checking out all the beautiful armies and painting contest entries and then suddenly you see something that makes you want to put 2 and 2 together and get awesome.
Horus above is done by Dave Taylor and part of Adepticon 40k Tournament Best General BushidoRedPanda's CSM army (counts as Abaddon). Providing the Emperor and the steps of Terra is Dakka's AgeOfEgos.
If only someone brought a slain Sanguineous the scene would have been complete! It is amazing that the two models are done by two different people. The scale and look of them both is perfect!