fragment custom_actor on Actor {
  __typename
  ... on User {
    id
    name
    login
  }
  ... on Organization {
    id
    name
    login
  }
  ... on Bot {
    id
    login
  }
}

query PullRequest($id: ID!) {
  node(id: $id) {
    __typename
    ... on PullRequest {
      author {
        __typename
        ...custom_actor
      }
    }
  }
}