Aldo Clemens is a former priest-turned-bartender who counseled Booth when he was a sniper during his days in the military.
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. 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.
- Aldo knew that Booth was the sniper that killed Radik who was first mentioned in The Soldier on the Grave back in Season 1.