A man who crushed a three-year-old boy to death with a car seat has been jailed for more than seven years.
Stephen Waterson, 26, inflicted irreversible brain injuries on Alfie Lamb, his girlfriend's son, who was in the footwell behind him in 2018.
Waterson initially denied manslaughter but changed his plea to guilty before a retrial in September.
Alfie had been at his mother Adrian Hoare's feet at the time. She was jailed for child cruelty in May.
Sentencing Waterson at the Old Bailey, Mr Justice Kerr described him as "cunning, manipulative, threatening, and controlling".
Justice Kerr said: "I do not find you were annoyed with Alfie and moved your seat back because of that annoyance."
But he said he was satisfied the nightclub worker from Croydon moved his car seat back twice "for your own comfort".
Described by police as "arrogant, selfish and deeply unpleasant", Waterson lied to detectives about what happened and threatened his girlfriend and two friends who were in his Audi convertible - along with a second child - on 1 February 2018.
Mr Justice Kerr sentenced him to five years and six months for the manslaughter.
He was handed a further two years for witness intimidation and 18 months for conspiracy to pervert the course of justice, which will run concurrently.
Alfie's death was the first time anyone in the UK had died from crush asphyxiation as a result of an electronic car seat, police said.
Hoare, 24, of Gravesend, Kent, watched as her son was crushed in front of her and then lied to protect her boyfriend.
She was sentenced to two years and nine months but cleared of manslaughter.
During her trial, prosecutors said Alfie was crying during the journey to Waterson's home after a shopping trip in Sutton, south London.
When he continued to moan, Waterson, who was in the front passenger seat, reversed his chair twice and said "I won't be told what to do by a three-year-old", Hoare told the jury.
The maximum space in the footwell was 30cm, and, at the touch of a button, that could be reduced to just 9.5cm, the Old Bailey heard.
Alfie collapsed in the car and died in hospital from his injuries three days later.
Hoare eventually confessed to her half-sister Ashleigh Jeffrey in a taped conversation handed to police.
Prosecutor Duncan Atkinson QC read out a victim impact statement from Ms Jeffrey.
She said: "He [Alfie] was always smiling. His death has had such a profound effect on my life."
"No sentence will be enough but today we finally gave Alfie a voice and justice has been done."
Barmaid Emilie Williams, 20, who had been in the car with Waterson and Hoare, admitted conspiring to pervert the course of justice after being threatened and "coerced" into lying by Waterson.
She was sentenced to five months imprisonment suspended for 18 months and 100 hours of unpaid work, to be completed after she gives birth.
Jurors in the first trial heard Waterson was a controlling womaniser who had a violent temper and three previous convictions for attacking an ex-girlfriend and his sister's husband.
His parents, who were in court for sentencing, refused to comment outside court.