@sidharthabahadur You have great input there. And you make a lot of valid points, although there are a few minor points which I feel that I should offer some clarifications on.
First of all, regarding the word "Mormon." It didn't come from Morgan. It originally came from the Book of Mormon, the sacred text which Joseph Smith translated from a set of golden plates. The ancient American scribe who compiled this text was named Mormon, hence the name of the book. The word "Mormon" was subsequently used as an epithet applied to anyone who joined Joseph Smith's Church of Christ (which was what the church was called before it was called The Church of Jesus Christ of Latter-day Saints). From Wikipedia (bold emphasis added, and my own notes in [bold italic brackets]):
The terms Mormonism and Mormonite were originally descriptive terms invented in 1831 by newspaper editors or contributors in Ohio and New York to describe the growing movement of "proselytes of the Golden Bible". Historian Ardis Parshall quotes a 1831 news item, appearing within the first year of the LDS Church's founding, as reading, "In the sixth number of your paper I saw a notice of a sect of people called Mormonites; and thinking that a fuller history of their founder, Joseph Smith, Jr., might be interesting to your community … I will take the trouble to make a few remarks on the character of that infamous imposter." [you can see that whoever wrote this original news article in the 1830s was hostile to Joseph Smith and the Latter-day Saints]
The term Mormon developed as a shortened version of Mormonite a year or two later. In all cases prior to 1833, these terms were used descriptively, despite nearly universal negative sentiment toward the movement. [the term was used as an abusive epithet] By the 1840's the term was adopted by Mormon leaders to refer to themselves, though leaders occasionally used the term as early as 1833. The term took on a pejorative meaning sometime before 1844 with the invention of the pejorative term Jack Mormon to describe non-Mormons sympathetic to the movement. Since that time, some have argued that the term Mormon has generally lost its pejorative status. [it has never truly lost its pejorative status because that was the context in which it was originally used]
Also, the concept of sainthood doesn't really exist in our doctrine. At least, not in the Catholic or Protestant sense of sainthood. Everyone who joins our church is considered a "Saint" in the sense that they are expected to follow the teachings of Jesus Christ and act accordingly. Hence the name by which we are called, "Latter-day Saints." The words "latter-day" refer to our belief that the Second Coming of Jesus Christ is going to occur in our time.
You are correct that William Morgan's wife (Lucinda) married Joseph Smith and was sealed to him. "Sealing" simply means that their marriage endured beyond the grave, different from typical marriages of "till death do we part." We believe that families and marriages can last forever and that is the only purpose behind the sealing rites.
That is also why we perform vicarious baptisms for the dead. William Morgan's wife probably specifically requested that the brethren perform a baptism for him because she wanted to be united with her husband after death (as she presumed he was dead). She probably actually planned on being married to both Joseph Smith and William Morgan by being sealed to him also in the temple (yes, women had multiple husbands at that time as well). It is interesting that he was the first person to receive this posthumous ordinance. Although, it's hard to say if Morgan was actually dead in 1841 or if he was already transformed at that time into his higher self (as documented in Etidorhpa).