Actor Adam Deacon sent his former mentor Noel Clarke a "barrage" of abusive messages via social media after the pair fell out over the title of hit film Anuvahood, a court heard.
Deacon, 32, allegedly called Clarke a "bully" and accused him of sabotaging his career in hundreds of "consistent and continuous" posts on Facebook and Twitter.
Once good friends, the pair stopped talking after a disagreement over the 2011 film Anuvahood, in which Deacon made his directorial debut and for which he won a BAFTA.
Hammersmith Magistrates' Court heard from Mr Clarke, who said he had helped to launch Deacon's career by selecting him to star in his films Kidulthood and Adulthood.
"I had an affinity for someone who was from the same environment as myself," he said.
He claimed that after the initial falling out, he began to receive abusive messages - including death threats - from Deacon via social media.
Mr Clarke, who is also known for playing Mickey Smith in Doctor Who, said: "We fell out in 2011 due to the fact that the films that I had made - Kidulthood and Adulthood - were very popular and in 2010 Mr Deacon asked if he could do a film which was a spoof of the film that I had done."
The court heard that Clarke initially helped Deacon work on this venture, but that their arrangement came to an end when Deacon signed a contract that cut him and his team out of the project.
"But I still supported him in this on the agreement that he would not call his movie 'Anuvahood'," said Mr Clarke.
He went on to say that although they verbally agreed on this, Deacon reneged and went ahead with the title.
Mr Clarke said that it was shortly after this that Deacon started posting abusive messages on social media, inciting violence against him and his family and posting pictures of his young family with an emoji of a gun.
The court heard the "real barrage" started in October 2014, and that although it caused Mr Clarke and his family "stress", he never responded.
Speaking of the messages, Mr Clarke continued: "They were abusive in nature, some calling me a bully, some saying I was sabotaging him. They went on to include inciting people to hurt me, and sent videos on Instagram."
Deacon also allegedly posted photos of Mr Clarke's seven-year-old child on social media, something that he had never done himself.
One photo, featuring Mr Clarke's young family and the message "you have to love family", accompanied by an emoji picture of a gun, was posted 81 times.
Mr Clarke alleged that one of the posts from Deacon said: "Kill the p***k on my ones - finding you today. Real talk."
"It is a death threat isn't it, really? If we are being honest," said Mr Clarke told the court.
He added that he was so worried about the content of the messages that he informed his children's school, which subsequently changed security codes around the building.
"You just don't know what is going to happen," said Mr Clarke.
The court also heard that even after Mr Clarke went to the police in November 2014, Deacon continued to post abuse, calling his fellow star a "snitch".
Under cross-examination, Mr Clarke denied that he had taken against Deacon for using the suffix "hood".
Deacon is on trial at Hammersmith Magistrates' Court, west London accused of posting abusive and threatening messages on social media relating to the Adulthood director.
The actor, from Bethnal Green, east London, who is also a rapper, played firearms officer Robbie in Channel 4 police drama Babylon which aired last year.
He is best known for playing main character Jay in the films Kidulthood and Adulthood, which saw him appearing alongside Mr Clarke.
He denies the charge.
The court also heard from Deacon, who asserted that he had not harassed Mr Clarke and claimed he seemed to "have it in" for him from the beginning.
"He would bully and belittle me on set in front of people - it would be a constant thing," the actor said.
He told the court he was only paid around £1,500 for his role in Kidulthood, despite being told by Mr Clarke that he would "make a lot more".
When asked by Hannah Smith, defending, why he had agreed to work on Adulthood, Deacon said: "He put a lot of pressure on me. He basically rang me up on the phone, saying I had to do the film otherwise the film wouldn't get funded.
"'Don't bite the hand that feeds you' - he used that a lot."
Deacon also claimed that Mr Clarke bragged about bullying his staff, and on one occasion called him "Judas" for going ahead with Anuvahood.
However, the actor admitted posting some messages on Twitter making reference to bullying, but that these were not directed at Mr Clarke.
"I didn't '@' him, I didn't mention him. That's why I'm so confused as to why there's a harassment charge," he said.
Referring to one post, Deacon said: "It was just a post saying 'stand up to bullies'. I am a firm believer in standing up to bullies.
"That is what Twitter is about. It wasn't harassment. This death threats, and pictures of guns, I didn't do that."
Deacon told the court he was "not bitter" and that he had simply used Twitter and Instagram to express himself.