TL;DR

The name MacGuffin does not originate from a particular person's name. It's just a nonsense term that has been around before it was applied to the movie concept of a random item that drives the plot.

Long answer

Tvtropes attributes Alfred Hitchcock with making the term MacGuffin famous, and Hitchcock himself names one of his screenwriters, Angus McPhail, as the creator of the word:

The term was popularized by Alfred Hitchcock, who credited one of his screenwriters, Angus McPhail, with the creation of this concept and the name for it, citing a particular school-boy joke:

A man is riding on a train when a second gentleman gets on and sits down across from him.
The first man notices the second is holding an oddly shaped package.
"What is that?" the first man asks.
"A MacGuffin, a tool used to hunt lions in the Scottish highlands."
"But there are no lions in the Scottish highlands," says the first man.
"Well then," says the other, "That's no MacGuffin".

Wikipedia gives a very similar story with additional background information, and giving various books about Hitchcock as the source of the information.

Hitchcock related this anecdote in a television interview for Richard Schickel's documentary The Men Who Made the Movies and for Dick Cavett's interview. According to author Ken Mogg, screenwriter Angus MacPhail, a friend of Hitchcock, may have originally coined the term.

It should be noted that the concept existed in movies before the term MacGuffin was coined for it:

The World War I–era actress Pearl White used weenie to identify whatever object (a roll of film, a rare coin, expensive diamonds, etc.) impelled the heroes and villains to pursue each other through the convoluted plots of The Perils of Pauline and the other silent film serials in which she starred.

We don't know for sure if the joke is the original source of the term, but it seems very likely. However there is no indication that there was any person named MacGuffin that was the source of this term.