In the OKR World, the CEO or the manager can create an OKR, while others can contribute to it. You can take a twin-way approach to have contributor(s) to an Objective and Key Result.
Contributor: He is a person who contributes to the completion and, thus, the success of the key result. Each contributor to a KR has a specific target of the actual KR. Once the contributor completes the set target of the KR, progress for the achieved target shows in the parent objective. The parent OKR is updated accordingly, too. Contributor(s) have a pivotal role in the success of the OKRs.
Collaborator: You find collaborators in the case of a Team OKR. In this type of OKR, an objective and a key result are assigned to the team. Not all team members are responsible for completing the OKR. Let’s take an example to understand the collaborator’s role better. If your team size is four and a Team OKR is assigned to the team with two members as contributors, the remaining 2 act as collaborators for that OKR. Though the remaining two members are a part of the Team OKR, they don’t directly contribute to it.