What planes are the key players in military airlifting?
I know the C-130J, C-17 and A400M are among them, what others are there?
What are the key differences between the above mentioned planes?
There is no single "key player". It depends on the task. You need big, long-haul transporters like the C-5 or the An-124 to move large amounts of troop and equipment quickly. This is called strategic airlifting and is done with turbofan-powered aircraft which are similar to airliners. But they need prepared and secured air strips of considerable length (the NATO standard airstrip is 8000ft long).
And then you need tactical transporters which can fly as close to the action as possible, and they must have STOL capabilities and defensive equipment to survive their missions. This requires mostly turboprop powered planes like the C-130, the C-160 or the An-12 for big equipment or the CASA 235 or the An-26 for smaller units or parts. The C-17 was meant to be a strategic airlifter with some tactical capabilities, but it cannot replace the smaller turboprops entirely. The A-400 and the An-70 are large tactical transports with some strategic capabilities, but this comes at the expense of usability on unprepared or improvised airstrips.
And then you need helicopters for the missions which require the highest amount of flexibility and closeness to the action.
All three depend on the other, and only together they become effective. That is why I cannot give you a key player.
Key characteristics of strategic transporters:
Key characteristics of tactical transporters:
Key characteristics of helicopters
In the past, the military has contracted a great deal of their airlifting, both of personnel and freight, to commercial carriers. If you include this activity, a number of other airplanes would have to be included, and of these, the 747 would be the workhorse of the group, especially in the 1990s. In addition to regular, ongoing military contracts and charters, they also had the CRAF (Civil Reserve Aircraft Fleet) program in which they subsidized the conversion of 747 pax aircraft to freighters with the proviso that if there was a CRAF activation, those aircraft and their civilian crews would be at the disposal of the military. Indeed, when Operation Desert Shield came along, there was a CRAF activation from 17 Aug 1990 to 24 May 1991.