Russian President Vladimir Putin's described former spy Sergei Skripal as a "scumbag" and a "traitor".
In March, Skripal and his daughter Yulia were poisoned by a nerve agent novichok in Salisbury - an attack which British intelligence has claimed was ordered by the Kremlin.
Russia has denied any responsibility for the attack.
Mr Skripal was a colonel within Russian military intelligence who served as a double agent for UK intelligence services.
He was convicted of treason in Russia and jailed, but in 2010 he was sent to Britain as part of a spy swap.
During an energy conference in Moscow today, President Putin directly slammed Mr Skripal directly.
He said: "I see that [media outlets] are pushing the theory that Mr Skripal was almost some kind of human rights activist.
"He was simply a spy. A traitor to the motherland. There is such a concept - a traitor to the motherland. He was one of those. He's simply a scumbag, that's all."
"He was caught, he was punished, he spent five years in prison, we let him go, he left and continued cooperating with, providing consultations to (foreign) security services."
Last month, police in the UK named two Russian nationals - who they believed to be Russian intelligence officers - as suspects in the investigation into the Salisbury poisoning.
Both men appeared on Russian state TV to deny the allegations.