Robbie was Martin's friend and the proprietor of Stern's Diner in Frankfurt that Martin frequented. Though they had a somewhat begrudging if teasing relationship, Robbie grew to know and care for his main customer, despite Martin's complaints about Robbie's inability to remember what his usual order was. He seemed to be aware of Martin's position as a criminal, but kept the knowledge in confidence.

Robbie came to notice a man (who he mistakenly characterized as "Vietnamese or Chinese") was frequenting his diner looking for Martin, which he pointed out to him—as it turned out, the man had come to find the location of the woman Martin was protecting: his one-time fiancee, Eva Heinemann. Later, Robbie would drive Martin, who had sustained a gunshot wound attempting to protect Eva from members of the organization he worked for, to be treated by the man—no less than the fugitive Dr. Kenzo Tenma—and heard Martin's story before he died in Dr. Tenma's care.

(Source: Monster Wiki)