It's the call that spurred an impeachment inquiry. On July 25, President Trump spoke with Ukrainian President Volodymyr Zelenskiy. The phone call would become the foundation of a whistleblower complaint alleging that Trump held up military aid for Ukraine to pressure Zelenskiy to investigate Trump's political rivals.

The rough transcript of the call released by the White House revealed that Trump did ask Zelenskiy about investigating a debunked conspiracy theory that alleges a Ukrainian company actually interfered in the 2016 election. He also requested an investigation of former Vice President Joe Biden and his son, Hunter. The rough notes detailing the talk were moved to a classified system reserved for highly sensitive information.

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The content of that call is now driving an impeachment probe, with questions about what exactly was said and what happened in the aftermath. Trump and Zelenskiy were not the only people on the line for the conversation. As is typical with head-of-state calls, a number of officials and staff members also listened in.

The White House has not released a full list of participants, but NPR has compiled a list of people identified so far.

President Trump

President Trump says this was the "perfect" call. He argues that there was no "pressure" on Zelenskiy to investigate anyone and that it was completely appropriate to ask about the Bidens. "READ THE TRANSCRIPT! I knew people were listening in on the call (why would I say something inappropriate?), which was fine with me, but why so many?" Trump tweeted on Oct. 29.

Volodymyr Zelenskiy
President of Ukraine

During the call, Volodymyr Zelenskiy was asked by President Trump to launch investigations that could help Trump in the 2020 election. In exchange, witnesses have told Congress, the White House was willing to facilitate engagement with Trump and the continued flow of military assistance. Zelenskiy, when asked in the open, has said he never felt "pushed" by Trump. But press reports suggest he felt pressure even before taking office.

Mike Pompeo
Secretary of State

Mike Pompeo was coy when reports first surfaced about the whistleblower complaint, but he eventually confirmed that he was on the July 25 call. He has defended the conversation. He told the New York Post that the call was "deeply consistent" with the administration's Ukraine policy. He says Trump asked about Joe Biden because he was concerned about corruption.

Timothy Morrison
Senior Director for European Affairs, National Security Council

Timothy Morrison was the top Russia official for the National Security Council at the time of the call, which he listened to from the Situation Room. He said the rough log of the call released by the White House "accurately and completely" reflects the substance of the conversation. Morrison said he did ask NSC legal staff to review the log of the conversation, because he was concerned the content might leak and affect bipartisan support for Ukraine. He said he did not believe that anything illegal was discussed.

Alexander Vindman
Top Ukraine expert, National Security Council

Army Lt. Col. Alexander Vindman is an Iraq War veteran who has served on the NSC since July 2018. He listened to the call from the Situation Room. He said he did not think it was "proper" to ask a foreign government to investigate a U.S. citizen. Vindman reported his concern to NSC's lead counsel.

Charles Kupperman
Deputy National Security Adviser

Charles Kupperman served as a top aide to then-National Security Adviser John Bolton. He left the administration shortly after Bolton's departure. The Washington Post reported that Kupperman was concerned about the call and the administration's handling of policy toward Ukraine. Kupperman has filed a lawsuit asking a federal court to determine whether he should comply with a congressional subpoena or with the White House order that he not testify in the impeachment inquiry.