It's the US, or at least Donald Trump and James Vance, sensing a business opportunity.
Many policitians and analyists have pointed out Trump does want the war there (and the one in Palestine) to end but also sees everything as a transaction that should end in his favour. It's a bit like wading into a lake to save someone from drowning, then sending him the clothes cleaning bill.
In theory Ukraine should benefit from a deal to sell minerals to the USA, but Trump sees it as the US benefiting from both the metals and the money. It is true that the USA has spent huge amounts of money on Ukraine's defence, but so have many other countries and they are not expecting repayments - they look beyond that.
The problem, and this appears to be what triggered that extraordinary shouting-match in the White House, is that Trump and Vance do not want to guarantee the US continue helping Ukraine protect itself from Russia, and started merely insulting Zelensky.
Now that the US President and Vice-President have had time to calm down, I wonder if they will think, or even care, how their behaviour will be seen around the world. Mr. Putin must be really enjoying what happened.