Which head of state sent the first transatlantic telegram?

A telegram of congratulation from Queen Victoria was sent to President James Buchanan at his summer residence in the Bedford Springs Hotel in Pennsylvania and expressed a hope that it would prove "an additional link between the nations whose friendship is founded on their common interest and reciprocal esteem." The President responded that, "it is a triumph more glorious, because far more useful to mankind, than was ever won by conqueror on the field of battle. May the Atlantic telegraph, under the blessing of Heaven, prove to be a bond of perpetual peace and friendship between the kindred nations, and an instrument destined by Divine Providence to diffuse religion, civilization, liberty, and law throughout the world." The messages were hard to decipher – Queen Victoria's message of 98 words took sixteen hours to send.

Victoria (Alexandrina Victoria; 24 May 1819 – 22 January 1901) was Queen of the United Kingdom of Great Britain and Ireland from 20 June 1837 until her death. On 1 May 1876, she adopted the additional title of Empress of India.

Daughter of Prince Edward Augustus and granddaughter of King George III, who both died in 1820, Victoria was raised under close supervision by her mother, Princess Victoria of Saxe-Coburg-Saalfeld. She inherited the throne aged 18 when her uncle, King William IV, died, by which time the United Kingdom was an established constitutional monarchy in which the sovereign held relatively little direct political power.