He was an S-class ninja who was as strong as the Three Legendary Sannin and was practically at Sannin-level. After a mission that ended in failure although he saved the lives of his comrades, Sakumo killed himself because his failure put the village and himself in a bad light. That is why Kakashi hated his father for what he represented. Whenever people heard the name "Hatake", they would pretty much look down on Kakashi. This attributed to Kakashi's over-achieving and perfectionism in his early days. Of course, Kakashi got over his father's shame and death and he adopted Obito's carefree lifestyle.