It's a bit more complex than what meow suggests. The problem is, by using "his" you are considered to be excluding all females - though this is a relatively recent opinion, and based on political correctness. Unfortunately English doesn't have a human-neuter pronoun ("it" clearly means something non-human), and attempts to create one have been messy at best. To clean up meow's sentence - I disagree with the his/her slash - how about: "Everyone is responsible for his or her own excellence and malevolence." That's still not as sharp as it could be - it still sacrifices the meaning of the sentence for "correctness". A common fix in modern English is: "Everyone is responsible for their own excellence and malevolence." Yes, "their" is a plural possessive, but thanks to PC it's becoming more commonly used as a singular, non-gender, human possessive (and "they" is used as a singular human pronoun). A bit shaky-sounding, but that's the best we've managed so far.

You can not use "he" after "someone"/"somebody"/"anyone"/"anybody You must use "he/she" or "he or she" I'd say: "Everyone is responsible for his/her own excellence and misfortune."