What is the subject of the following sentence?
All he does is invite random strangers on the internet to play games with him.
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Sign up to join this communityWhat is the subject of the following sentence?
All he does is invite random strangers on the internet to play games with him.
The subject is the noun phrase "all he does," which consists of the pronoun "all" modified by the reduced relative clause "he does."
(If you're a fan of Huddleston & Pullum (2002), you can say that all is not a pronoun but a determinative serving as a fused determiner-head.)
As the other answer says, the subject of the sentence is grammatically "all he does". But the sentence is essentially equivalent to
He only invites random strangers on the Internet to play games with him.
In this reformulation, we can see that the subject performing the action is "he". It's just a more awkward way to phrase it, and doesn't emphasize the exclusivity that "all he does" suggests.