All 350 characters (and counting!) that appear in Hitman (2016), Hitman 2 and Hitman 3 in various roles and capacities; all can be found in the below compiled list of pages. Characters often re-appear in each game or are referenced in subsequent entries to some degree.
Expect unmarked spoilers for the first two games (their story beats are considered common knowledge In-Universe, or otherwise make it tricky to talk about in the context of later games) and for Agent 47: Birth of the Hitman (which opens with a massive Hitman 2 spoiler that is impossible to avoid talking about) , but there are marked spoilers for Hitman 3 on all pages.