I think I am a verb instead of a personal pronoun. A verb is anything that signifies to be; to do; or to suffer. I signify all three.

Grant’s quip plays on grammar to describe a life defined less by self-assertion (“I” as a pronoun) than by action and endurance (“I” as a verb). By invoking the old schoolbook definition—“to be; to do; or to suffer”—the line compresses three roles he likely felt he had inhabited: existing under public scrutiny, acting decisively in war and politics, and suffering the costs of command, controversy, and personal hardship. The humor is self-deprecating but also quietly proud: it frames identity as something proved through deeds and trials rather than claimed through rhetoric. In a quotations context, it is often used to characterize Grant’s plain style and emphasis on practical results.