Sykes is the manager of the Whale Wash where Oscar is employed. He and Oscar have a history before the movie is introduced; due to Oscar's constant get-rich-quick schemes, he owes Sykes over five thousand clams in debt and Oscar doesn't appear to be bothered by this.
We learn that Sykes is also employed as a henchman for Don Lino, the head of a mafia group of sharks. It is revealed here that, much like he and Oscar, Sykes and Don have a history together, as the latter is quoted by saying, "Now, you and me, we worked together a long, long, long time."
Sykes' constant interruptions and neurotic wincing did not make for such a smooth meeting, and this did not improve when Don Lino mentioned that his two sons, Frankie and Lenny, will someday run the reef. While comfortable with being under Frankie's command, Sykes was skeptical in working for Lenny.
Ultimately, Sykes is fired by Don Lino after disrespecting Lenny's effiminate behavior.
Under pressure from his recent termination, Sykes orders Oscar to take the five thousand clams to the racetrack the next day in order to pay for Don Lino's protection (and also so that he would not order an attack on the Whale Wash).
The situation gets rocky when Oscar blows the five thousand clams on a seahorse instead of paying it directly to Sykes. After blowing up, literally and figuratively, he commands Ernie and Bernie (his own henchmen) to, "put him in the deepest hole in the ocean."
Later on, after Oscar's bogus story about murdering Frankie, Sykes (without the knowledge of the truth behind the lie) becomes his manager and spends his time partying with Oscar. He appears to let his position go to his head, claiming to be 'untouchable'.
Everything appeared to be fine for Sykes while Oscar was famous, but things began to go downhill after Don's sharks kidnapped Angie, the receptionist at the Whale Wash and Oscar's love interest. It is here that Sykes finally discovers the truth behind Frankie's death through Lenny's not-so discreet confession.
Now back to his neurotic, wincing old self, Sykes accompanies Oscar and Lenny (disguised as a dolphin) to a sit-down with Don Lino's mafia group. This leads into a drawn-out battle between Oscar and Don Lino, which ultimately ends in the Whale Wash.
During the films epilogue, Sykes and Oscar are now co-owners of the Whale Wash, which has become frequented by both whales and sharks. He appeared to have been inspired by Oscar's sassy behaviour as he tries to scat with Don Lino.
Sykes is viewed as being very neurotic and easily stressed with a short temper. This is shown whenever he inflates to a large size, either through worry or rage. Sykes also winces and stutters whenever he finds himself in a pressing situation. He is seen as being quite insecure with his emotions and he easily lets his anxiety get the better of him. As well as this, Sykes appears to be quite a cowardly character as he finds it hard to stand up to Don Lino even though he should be used to the latters blunt attitude.
Much like Oscar, Sykes easily lets situations and positions get to his head. This is shown when he becomes Oscar's manager and he becomes so egotistical that he is willing to berate Don Lino and claim that he is 'untouchable'. He even tells Lino that he needs to start paying him protection.
Despite all of his negative traits, Sykes is not entirely bad. He is actually quite a humorous character and he, along with Ernie and Bernie, provides a lot of the film's humor. As well as this, he appears to be very loyal to his friends, such as when he is willing to protect Oscar despite his learing about his over-emphasized lie. Deep down inside, Sykes seems to be a nice guy as he instructs Ernie and Bernie to go easy on Oscar after banishing him to the Wastelands.
Sykes is also, apparently, well-organized, although this is most likely just said by Oscar so that he would get out of paying for his various debts.