Man in leather uniform with helmet: Obelix

1st: Home; 2nd: by Rembrandt (1642); 3rd: by Lundens (1649).

Only part of a large belly in a leather outfit and the top of a helmet are visible here.

In the copy by Lundens, it becomes clear that the helmet is metal and carries a generous plume. In the original painting, only a small piece of plume can be seen, and the material of the helmet is unclear.

This is enough to tell us that someone is standing in the background, that he belonged to the civic guards, and that he either did not pay or was invented by Rembrandt. Both options seem equally plausible.

Rembrandt may simply have needed a few extras to strengthen the impression of an advancing company. A full company consisted of about 120 men, after all.
This faceless, portly shooter appears to have been added purely as stuffing material, a role he fulfills with admirable dedication. Hence my nickname for him: Obelix, after the character in Goscinny's and Uderzo's comic album series.