I guess Steele would be the more obvious answer.   Weeks before the 2016 Presidential election, Strzok's team agreed to pay former MI6 agent and Fusion GPS operative Christopher Steele $50,000 if he could verify his claims that the agency had already used to take action. Of note, Fusion separately paid Steele $168,000 to assemble the dossier which had the cooperation of two senior Kremlin officials. https://www.zerohedge.com/news/2017-12-03/anti-trump-fbi-agent-fired-mueller-probe-relied-russian-dossier