Tracking the original agent

We're setting up a support process where the first agent to whom the ticket is assigned is the "tier 1" agent, and that agent may later escalate the ticket by assigning it to a Zendesk group or a person who is a subject matter expert. In our process, the ticket is now in "tier 2." 

This has raised a key question: How can the tier 1 agent create a view that shows all tickets for which they were the initial assignee?

I tried creating a custom ticket field called "tier 1 agent name," but it looks like I can't automatically set this value with a macro, so that probably won't work. Any other thoughts on how I might be able to accomplish this?