The Delta IV and Delta IV Heavy are a direct copy of its real life counterpart. There are two main versions in real life, both of which are completely replicable in-game. These are the Delta IV and the Delta IV Heavy.
The Delta IV Heavy is most likely the more prominent of the two in-game, due to its large payload capacity and iconic Delta IV boosters. It can launch pretty much every payload you can think of, besides the Station Module Large. In those cases, it is still possible with an extra stage such as a tug module. The Delta IV is compatible with the Orion Command/Service Module.
This is the Delta IV heavy-Orion Configuration:
The Delta IV variant however isn't nearly as reliable and useful as the Delta IV Heavy, but it works.
The Delta IV Medium Configuration:
-Payload and fairing