Author: Enrique Dupuy de Lôme, Spanish Ambassador to the United States.
Recipient: José Canalejas, Spanish Foreign Minister.
Leaker: Cuban revolutionaries (identity remains unclear).
Publisher: William Randolph Hearst, owner of the New York Journal.
The De Lôme Letter criticized President McKinley for being weak and catering to public opinion regarding the Cuban situation. It called him "weak" and accused him of wanting to appease both sides.
Yes, there are multiple cartoons satirizing the phenomenon of yellow journalism. A notable example is an editorial cartoon by Leon Barritt for the June 1898 issue of 'Vim' magazine. The cartoon shows Joseph Pulitzer and William Randolph Hearst both attired as the Yellow Kid comics characters and competitively claiming ownership of the war.