noun
bossy person; self-appointed manager; bossyboots
Colloquial, mildly derogatory term for someone who takes charge without being asked, often organizing or directing others in a pushy way.
彼はいつも仕切り屋で、みんなの予定まで決めたがる。
He's always a bossyboots, wanting to decide everyone's plans.
あの仕切り屋がまた会議を仕切っている。
That self-appointed manager is running the meeting again.
Means 'meddler' or 'pushy person', focusing on intruding into others' affairs. 仕切り屋 emphasizes taking control and organizing, not necessarily meddling.
Compound of 仕切り (managing, partitioning) from verb 仕切る and suffix 屋 (person with a trait). Literally 'a person who manages/partitions', used for someone who bossily takes charge.