Alfred Petersen, around the time he changed his name to Alva MacLaughlan, circa 1914 in Chicago. He'd already started smoking his signature cigars. Click the photo for an enlargement.
Baby Tom, left, and older sister Marie, late 1916. Click to enlarge.
Marie Jatho MacLaughlan with Tom, about 1919 in Chicago. Click the photo for more details.
Alva Elwood MacLaughlan was born in Chicago on March 24, 1894...but that wasn't his birth name. If you have Alva in your family tree and have been trying to trace the family's roots to Scotland, look toward Denmark instead.
Alva was born Alfred Emil Petersen in Chicago to Hans and Catharina Petersen, both of Danish heritage from Schleswig-Holstein. Alfred was the middle child of eleven, the rest of whom kept the surname Petersen, and was named for his maternal uncle Alfred (originally Peter Edlef) Petersen of Omaha.
Alfred's transformation first appeared in his Cook County marriage
license from 1914. 
In
1916 at son Thomas' baptism
he was listed as Alfred Petersen-McLaughlin; at left (click to enlarge) he's seen holding
either baby Marie or Thomas.
He was Alfred Edward McLaughlin in 1917 when registering for World War I. At his second son's birth he's Alfred Emil McLaughlin (and so was his son). In several newspaper articles from the 1920s through the 1940s he used his first two initials and the surname MacLaughlan (his preferred spelling). In the 1930 census he was (probably mistranscribed) Alba McLaughlan. By 1935, when registering for the Social Security program, he listed Alva Elwood MacLaughlan as his name, altering his parents' names on the document as well.
Why the name change? Several stories coexist. His Petersen clan believed that Marie wanted to marry an Irishman...so obligingly he became one. Marie's family thought the name change was from McLaughlin (Irish) to MacLaughlan (Scots) to avoid anti-Irish sentiment.
Most likely it was actually anti-German sentiment during WW1, which could affect anyone vaguely assumed to be German. It was a puzzlement to his Petersen family but as his mother Catherine once put it, "Alfred just wanted to be Irish". Maybe that's the best explanation.
Alva was a bookkeeper, his wife Marie a homemaker. They had four children (Marie, 1915; Thomas, 1916; Alfred/Alva, 1920, and Dolores, 1929), all born in Chicago, though the family traveled by car and resettled in other towns during the 1920s where Alva was trying out new business schemes. They eventually resettled in California around 1946. Marie died in 1956 near Barstow, California, where the couple had recently bought a hotel to manage. Alva, while working as a security guard in Whittier, died in 1957 of a heart attack. His death certificate maintained the illusion that his parentage was unknown...until now.