Frederick Crist Trump Jr. (October 14, 1938 – September 26, 1981) was an American airplane pilot and maintenance worker. The eldest son of real-estate businessman Fred Trump Sr., he fell out of his father's favor and became an airline pilot instead of taking over the family business, leading to his younger brother Donald doing so instead. Both Fred Sr. and Donald disparaged Fred Jr. By the early 1970s he could no longer function as a pilot due to his alcoholism, a condition which also contributed to his fatal heart attack.

Frederick Crist Trump Jr. was born on October 14, 1938, as the first son of real-estate developer Fred Trump and Mary Anne MacLeod Trump in Queens, New York City. In 1956 Fred Jr. graduated from St. Paul's School, a college preparatory academy for boys. In that same year his father, Fred Sr., donated money to have the playing fields redone which in his honor were renamed Trump Field.

Trump attended Lehigh University and joined a historically Jewish fraternity, Sigma Alpha Mu, although he was not Jewish. In 2018, psychoanalyst Justin A. Frank asserted that Fred Jr. joined a Jewish fraternity to rebel against his father—who was, Frank alleged, anti-Semitic. (In 2020, Fred Jr.'s daughter, Mary, accused Fred Sr. of being "quite anti-Semitic".) Fred Trump Jr. became president of the fraternity and graduated with a Bachelor of Arts in business, also completing Reserve Officers' Training Corps and entering the Air National Guard as a second lieutenant.

In 1958, Trump met Linda Clapp while vacationing in The Bahamas. She later became a flight attendant and asked him for help finding an apartment near Idlewild Airport; they soon began dating. He proposed to her in 1961. In early 1962, they were married in Florida, and she resigned from the airline, which did not allow its flight attendants to be married. They settled in Manhattan and had their first child, Frederick Crist Trump III, in November 1962. The next year, they moved into one of Fred Sr.'s apartments in Jamaica, Queens. During this time, Trump did maintenance jobs on his father's properties.

Fred Sr. wanted his oldest son to be "invulnerable" so he could take over his real-estate business, E. Trump & Son (later known as the Trump Organization), but Fred Jr. was the opposite in personality. In 1966, Fred Jr. was listed in newspapers as vice president of the company, but he had a difficult time working with his father. That same year, Fred Jr. left the company to pursue his dream of being a pilot, quickly being accepted at Trans World Airlines, which created tension with his father. According to Fred Jr.'s daughter, Mary L. Trump (born 1965), her grandfather "dismantled him by devaluing and degrading every aspect of his personality." She said Fred Sr. and Donald mocked him for his decision to become an airline pilot, comparing it to being a bus driver or chauffeur.

By 1970, after a series of domestic incidents, Clapp asked Trump to leave their home and arranged for Fred Sr. to change the locks. When his alcoholism prevented him from continuing to function as a pilot, Trump returned to work for his father's business. He eventually moved into the unfurnished attic of his parents' house and again did maintenance on Trump properties. On September 26, 1981, at the age of 42, he died from a heart attack caused by his alcohol use.

Donald Trump, who since 1976 has spoken publicly of his own abstinence from alcohol, initially cited the formative influence of their father's teetotalism, but also included experience with his brother, saying:

"Every day he lectured me, 'Look at the mess I'm in. If I ever catch you smoking, you'll be sorry, drinking even a glass of booze because you'll like it too much.' ...Freddy did a good job."