The rich man (10:22) was a young ruler (Matthew 19:20; Luke 18:18). He showed respect toward Jesus by kneeling and calling him Good Teacher.
Teacher is a common title for Jesus in Mark (see Mark 4:38; 5:35; 9:17, 38; 10:20, 35; 12:14, 19, 32; 13:1; 14:14). The addition of good is unique.