Alexander Neibaur was the first Jewish man to join the newly founded LDS faith and became a good friend of the Prophet Joseph Smith. He even assisted in teaching Hebrew to the young Prophet. Neibaur reportedly wrote one of the eight early published accounts of Joseph Smith's First Vision of the Father and the Son.
A firm believer in the Prophet, Neibaur wrote the following lamentation on the martyrdom of the Prophet.
All this heaviness has reached us;
Can any one ne formed to declare
What has befallen us?
All this we bear, and the name of our God
We will not forget, nor deny,
The 'Hebrews' God' he is called,
Thou art clothed with righteousness,
But we are vile.
(History of the Church, Volume 7, p. 192)
Neibaur also composed the hymn "Come Thou Glorious Day of Promise".
Neibaur's daughter Rebecca married prominent LDS author Charles W. Nibley. This makes Neibaur the great-grandfather of famous LDS scholar Hugh W. Nibley.
Alexander Neibaur is buried in H-3 in the Salt Lake City Cemetery, just east of the offices.
For more information, see his Find A Grave memorial as well as his Wikipedia entry.