Alexandre de Rhodes was a Jesuit priest, most famous for his work in Vietnam.
Born in France in 1591, he joined the Jesuit order as a missionary, and ended up in Hanoi as Vietnam's first (but certainly not last) Frenchman around 1619. There he began his life's work, and while he converted many Vietnamese locals to Christianity and wrote the first Vietnamese catechism, his most lasting effect was on Vietnamese writing. A gifted linguist, he mastered Vietnamese in only 6 months and compiled the first Vietnamese-Latin dictionary, and was one of the first to attempt to Romanize the Vietnamese alphabet. Today the national language of Vietnam, Quoc Ngu, is based on his original transliterations and phonetic work.
Rhodes's missionary work was constantly at odds with the local pagan priests, particularly with regards to ancestor worship, something that was frowned upon by Jesuit teachings, and by preaching God's equal love, which clashed with the predominant Confucian hierarchical system. He was exiled twice and nearly sentenced to death for his teachings in the city of Hue. His other mission work in China and Macao were more successful, but his true love was with the Vietnamese people. He was finally permanently banished by the Vietnamese overlords in 1645. Upon his return to Rome, he begged for more money to do further expeditionary work in Vietnam, but was instead sent to Persia.
Finally in 1658 his plan was approved, but by then Rhodes was too ill to travel back to Vietnam himself - he died two years later, never returning to his "land of the birds." Still, his oft-exaggerated tales of rich veins of gold, spices, and silk "used as fishing line" in the nation kept the French interest in Indochina elevated for several more years - enough to lead to its eventual colonization, according to some scholars.
His tale is probably best gleaned from his own diary, which you can find along with annotation and analysis in a book by Solange Hertz.