Besides portraying himself, Beckmann painted his wives -- especially his second wife -- and a number of these paintings are shown below.
His first wife was Minna Beckmann-Tube (1881-1964), Wikipedia entry here, who was about three years older than him, and a fellow art student. He insisted that she abandon art after their marriage, so she took up opera singing. She was mother of his son, and they remained friends after he dumped her.
Minna's replacement was Mathilde (Quappi) Beckmann (1904-1986), German Wikipedia entry here, 20 years younger than Beckmann. Quappi was a daughter of the important Munich painter Friedrich von Kaulbach.
There might have been more complications, but let's turn to the paintings.
Publicity image of Minna.
He painted this around the time their marriage ended.
Probably taken during the late 1920s.
Beckmann emphasized her nose in his early portraits, then dialed that down by the 1940s.
For some reason the date for this seems wrong. Her hairdo is more appropriate for towards the end of the decade.
I think this is Beckmann's best portrait of her.
In the upper-right corner Beckmann notes this was painted in Amsterdam where they lived from 1937 to 1948.
Image slightly cropped at the bottom.
Painted in St. Louis. Like Beckmann, Quappi was a smoker.