The gentleman to the right is Gustave Koerner. He was the man largely responsible for getting Chicago picked as the place for the May, 1860 Republican Convention. He was also of German ancestry, and helped build German support for Lincoln.
Koerner was once a Democrat, but left that party in disgust when they became affiliated with such movements as the Know Nothings, the race-baiting party of the time.
He was Lieutenant-Governor of Illinois, and next in line to become Governor if Joel Matteson, then chief executive of Illinois, won his Senate race.
In the 1840s, he had been a judge, and had met Abraham Lincoln during that time. He and another judge-turned-politico, Lyman Trumbull, pulled every available string (and some that were not so readily available!) in New York, where a group of Republican Party leaders met to choose the sight of the 1860 Convention.
It was much like Goldilocks & the 3 Bears--one city was too small, another was too expensive, but Chicago was "just right." Plus Chicago promised to build a special hall in which the electors could meet.
Why does it matter where the convention was held? There were many steps forward in getting Abraham Lincoln elected President. Moving the Republican Convention out of Seward territory was a particularly large step.