The manuals for Sonic Wings 2 explain that Captain Silver is fighting to avenge the death of his friend Randy, who was also the original owner of Flint the parrot. Randy is also described as Silver's comrade, indicating that they probably fought together in the United States military. In some game endings, Silver mentions having fought for Randy's sake.
Although these endings imply that Randy really is dead, he is shown as still alive in SWS/SWL if the player defeats Lar (or Do-ni Revision) with Silver in single-player mode. Silver and Flint go to visit Randy's grave; however, Randy himself shows up too. Silver is understandably surprised, but Randy explains that he really is alive, and they have a joyful reunion. In fact, both Japanese and English versions of the scene describe them as "liv[ing] happily ever after."
It is not explained how Randy is still living, or why he waited so long to let Silver know. One possibility is that he was captured by Fata Morgana and was unable to escape until Silver defeated Lar. To add to Randy's mystery, he is only shown in silhouette.
Hawk from Sonic Wings Assault was originally intended to be Randy's son. This version of Hawk was going to be strongly attached to Silver, apparently as a surrogate father figure. However, Hawk's design was changed and this plot line was abandoned.
Randy is based on the character Charlie Nash from the Street Fighter series. Charlie has a similar hairstyle and an upturned collar, which accounts for Randy's strange silhouette. The similarities between the two characters are even more apparent when Charlie is brainwashed and appears as Shadow.
Charlie's relationship with the Street Fighter character Guile is similar to Randy's relationship to Silver, although Guile and Silver themselves are very different characters (with very different hair, or lack thereof). Like Silver and Randy, Guile and Charlie fought together (although Charlie was Guile's superior) and were best friends. Charlie was also supposedly killed by the enemy, leading Guile, like Silver, to seek vengeance. At the end of Sonic Wings Special and Limited, Silver is shown visiting Randy's grave, as Guile visits Charlie's in Street Fighter II.