Sam Singleton is a customer of Napolean House.
Gabriel has known him and Markus for some time, but only from seeing from time to time at the Napolean House.
Around 1943 he had a Voodooienne make a charm for him, which he buried under the front porch of a girl he wanted to approach. The next day he talked to her and the poor guy eventually married her.
Since 1973 he daily visits the Napolean House to play chess with Markus, and he always loses, as Markus psychs him up.
On Day 3 Gabriel Knight told him that Markus perhaps uses Voodoo to win him, and he offers him a Master Gamblin' Oil from Dixieland Drug Store, which Sam drinks with a Pimm's Cup. Indeed he finally wins Markus for the first time after 20 years, and Markus leaves enraged. Sam offers Gabe a favor, and Gabe gives him a clay mold of Madame Cazaunoux's snake bracelet.
On Day 4 he brings Gabe a replica.