I figured I'd take Frances' hint and post on Andrew Jackson Donelseon, another one of the Jacksons' "children." I posted on his first wife, Emily, earlier (as a note, they were first cousins). When I was writing on Andrew Jackson, Jr., I actually kept finding things on Andrew Jackson Donelson in any case!
You can find entries on him in both the Tennessee Encylopedia and the Handbook of Texas. Andrew Jackson Donelson was the nephew of Rachel Jackson and spent part of his early life at the Hermitage:
Andrew Jackson Donelson, son of Samuel and Mary Donelson, was a soldier, lawyer, politician, and diplomat. After his father's death around 1804 and his mother's remarriage, Donelson was reared at the Hermitage, home of his aunt, Rachel Donelson Jackson, and his namesake Andrew Jackson. He graduated from West Point, second in his class, and served as General Jackson's aide-de-camp during the Seminole campaign. After this conflict, he resigned from the army and studied law at Transylvania University in Lexington, Kentucky.
In 1823 Donelson returned to Nashville to practice law and within the year married his first cousin, Emily Tennessee Donelson. He inherited his father's property adjacent to the Hermitage, and the Donelsons had their home, Tulip Grove, constructed while they were in Washington with President Jackson during most of his two terms. Donelson served as the president's private secretary, and Emily acted as the official hostess of the White House. Emily died of tuberculosis in 1836, shortly after Tulip Grove was completed, leaving four small children. Donelson remarried five years later and had eight more children with his second wife, Elizabeth Martin Randolph.
As Frances noted, Andrew Jackson Donelson played a crucial role in the annexation of Texas into the US:
In 1844 President John Tyler appointed Donelson chargé d'affaires of the United States to the Republic of Texas. His duties were to present American propositions to President Anson Jones and to further the cause of annexation of the republic to the United States. Donelson performed both tasks with skill and diplomacy. In March 1845, while he was temporarily in New Orleans, Congress passed a joint resolution admitting Texas to the Union, provided that the state adopt a republican form of government before July 1846. On April 12, 1845, Donelson interviewed President Jones, and on April 15 Jones called Congress to meet on June 16, 1845. Jones presented the proposition of the United States, and the offer was accepted unanimously. A convention was called to meet on July 4, 1845, and the ordinance accepting the terms outlined in the joint resolution of the United States Congress was passed the same day. Donelson was given a certified copy of the ordinance, which he forwarded to the secretary of state.
The Texas State Library and Archives Commission has an online exhibit on the annexation of Texas and it includes information on Andrew Jackson Donelson's contributions and two original letters written in the period (both scanned images and transcripts are available). One is Ebenezer Allen and the other is to Sam Houston.
This was not the end of his career though:
His success in this undertaking [annexation of Texas] led to his appointment as minister to Prussia from 1846 to 1849. In 1851 he became editor of the Washington Union but left this position as the Democratic Party moved toward sectionalism.
Donelson ran for vice-president on the Millard Fillmore ticket with the support of the Know-Nothing Party in 1856. Their loss ended his national political career. In 1858 he sold Tulip Grove to Mark Cockrill and moved his family and his law practice to Memphis, where he remained active in local politics. He died in Memphis in 1871.
As you can see, Andrew Jackson Donelson had an interesting life!