Possible Clues:

• Absurdist play's absentee
• The unseen hero sought by Beckett's Vladimir and Estragon?
• Character waited for leave period
• Play guy ''sure to come tomorrow''
• One expected in vain
• Title character who never appears onstage
• Absentee title character
• Beckett title character who is not in the cast
• He 'won't come this evening but surely tomorrow'
• Whom Vladimir and Estragon were waiting for, in a Beckett play