Aldo Clemens is a former priest-turned-bartender who counseled Booth when he was a sniper during his days in the military.
Aldo: I used to be Booth's confessor when he was a Ranger. Me and him are having a tough time breaking the habit even though Booth's the reason I quit being a priest and decided God was my worst enemy.
Brennan: God is a myth.
Aldo: No, I don't think so. I think he's a bastard.
Brennan: Booth was a sniper. He asked for forgiveness from you every time he killed somebody?
Aldo: Through me, technically. You can imagine why a guy might get "soul-sick" providing absolution.
Aldo met Booth in the military where he was an army chaplain. He helped and counseled Booth during his sniper assignments for years, but eventually got "soul sick" and quit being a priest, with Booth being his last confession. After that, Aldo began working as a bartender.
Eight years after leaving priesthood, in The Secrets in the Proposal, Aldo is the one person Booth trusts with the truth, and confesses to him that he rejected Brennan's marriage proposal due to Christopher Pelant's interference. Aldo later is the one that convinces Brennan that Booth broke off their engagement for a good reason, and tells her she should have faith in him. He once again gives Booth and Brennan support and advice regarding Pelant in The Sense in the Sacrifice.
In The Woman in White, Aldo performs Booth and Brennan's wedding ceremony after becoming a priest again through the internet.
In The 200th in the 10th, he appears as an inspector from Interpol.
Aldo is the victim in The Price for the Past. Brennan identified his remains from a combination of military-related injuries, frequent, prolonged kneeling, remodeled ear fractures, and a partial facial reconstruction. They discovered that he became a heroin addict and was fired from the bar for stealing from the tip jar. The manner of Aldo's death was a suicide which Booth considered "a sacrifice". Aldo fractured his own neck after suffering a medieval form of torture inflicted by someone connected to Josip Radik (one of Booth's military kills), ending his suffering and presumably preventing him from giving the torturer Booth's name.
It was eventually discovered that the killer is Mark Kovac, the son of Josip Radik, who wanted to kill Booth for killing his father in Bosnia in 1995. In The End in the End, Booth kills Kovac and avenges Aldo's death.
- Aldo knew that Booth was the sniper that killed Radik who was first mentioned in The Soldier on the Grave back in Season 1.
- Cam stated that Aldo never stopped believing in God, but his belief no longer comforted him after what he saw during his time in the military.