sui

The reflexive pronoun, cited by its genitive "sui" because it has NO NOMINATIVE at all: a reflexive can never be the subject, since it exists only to point back at one. The forms you will meet are "se" (accusative and ablative), "sibi" (dative) and "sui" (genitive), and each covers singular and plural and all three genders at once, so "se" is himself, herself, itself and themselves alike.

It refers back to the SUBJECT of its own clause, which is what separates it from "eum" and "eam". "Se vidit" is he saw himself; "eum vidit" is he saw him, some other man. In indirect statement, "se" points back to the person doing the speaking, which is why "dixit se venturum esse" is "he said that HE would come".

With "cum" it goes on the back of the preposition: "secum", with him.