In the beginning of the series, Isshin is portrayed as a silly, fight-loving father who takes a keen interest in what his children are doing, but does it either offensively or with an all-too-happy tone, which elicits comical reactions from his kids, usually in the form of a kick. Isshin also seems to enjoy making fun of Ichigo and has a tendency to talk to the large memorial poster of his late wife Masaki, which he has pinned up in their kitchen, whenever he feels particularly emotional. Isshin is a big fan of Don Kanonji's TV show.
Despite his outrageous guise, however, Isshin can be serious and grim at times. On the date of Masaki's death, Isshin smokes a single cigarette in front of her grave, since she thought it made him look cool. He reflects that it was the first and last time she ever complimented his appearance. He also told Ichigo that he shouldn't blame himself for his mother's death because she gave her life to protect him. In addition, during his confrontation with the arrancar Grand Fisher and the subsequent chat with Kisuke Urahara, he remains completely serious (aside from a short argument between him and Kon about his parenting, and another, albeit short, between him and Urahara after the latter likens him to his son).
Isshin appears to be an associate of Kisuke Urahara and possesses knowledge of Sousuke Aizen's alliance with the Menos. He mentions in his conversation with Urahara that he encountered arrancar about ten years before the main storyline, though they were nowhere near as complete as Fisher. He also reveals to Kon that he has been aware of Ichigo's shinigami activities and Kon's substitutions since Grand Fisher's first attack. He also notes that he has never called Kon "Ichigo" while Kon is in Ichigo's body and that the traveling charm he gave Ichigo before he went to rescue Rukia was actually for Kon (it's a protection talisman). This shows the sensitivity and propriety that he possesses of his role as Ichigo's father, which is rarely portrayed in the series.
Isshin also shares a relationship with Ryuuken Ishida not unlike that of their sons. When Ryuuken discovers his son is missing, Isshin pays him a visit and the two chat about their respective styles of parenting. It is then revealed that Ryuuken was aware of Isshin's status, and he comments on Isshin's powers. The two have some prior history together, and that they have been acquaintances for quite some time. It can also be noted they both are doctors, Isshin runs a clinic while Ryuuken runs a hospital. There have been hints that the two cooperate on a professional level, with Isshin handling minor cases, and occasionally requesting aid from Ryuuken.
(Source: Bleach Wikia, Bleach Official Animation Book VIBEs)
The Gotei 13 are the protectors of Soul Society, organizing the Shinigami into a military. Each of the 13 divisions is led by a captain, all of whom are a force to be reckoned with on any battlefield. Let's meet these Gotei captains!