Alex Ferguson told the Ryan Giggs trial that the ex- footballer had a great temperament.
Sir Alex said he was the best example at the club, and everyone looked at Ryan Giggs as the number one.
The ex-Manchester United player denied controlling behavior.
Mr Giggs is accused of hitting Ms Greville's sister Emma.
The incident is said to have taken place at the home of the former Wales international and manager on 1 November 2020.
His love notes and poems have been read out in court.
The court heard that in one instance, he told Kate Greville that she was the jam in his doughnuts.
"To have a career as long as he had in a difficult position, in terms of energy, he fulfilled everything we ever wished for," Sir Alex said as a defence witness.
Sir Alex said that they went to his house to convince him to join Manchester United. My assistant and myself.
Did you know him when you were a kid?
His main contact was his mother. She was very pleasant to be around. It was very easy. Ryan was not loud. He just listened to what was being said. His mother did all the talking.
They talked about the club's ambitions.
When Sir Alex arrived at the club, they had been through a bad period. We had a lot of work to do. Ryan was one step in the right direction for young players.
He said the player got into the first team at the age of 17 after signing a schoolboy form.
It was the first time we had to think about looking after him.
He was being compared to George Best. A lot of attention was given to the boy.
I told his mother that I would look after him if she trusted me.
They had to come through me. He was protected by us.
It's important when someone says you're the next George Best. The boy was fine.
Any media that wanted to do an article had to come through me.
Sir Alex was asked if he was aware of Mr. Ryan's girlfriends.
He would bring a friend with him to dinner at the end of the season.
He said that Mr Giggs played for Manchester United from the age of 17 to 41.
Sir Alex said that he used Ryan as an example when he lost his temper about performance.
I knew he could take it even though he got the end of my tongue.
Everyone in the dressing room would think that they could all take it.
Messages and poems between the ex- player and Kate Greville were read to the court.
The morning was beautiful on November 6th. I am hitting people. You are absolutely amazing.
Ms Greville said that she wasn't punching. You are the epitome of rock and roll. You have the best butt on the planet. You are an amazing person.
Ms Greville wrote "You know I think you are amazing." I love you.
"Fandabidoozie" was the reply. You are the ingredients in my food and drink.
Ms Greville said that she and her husband were going to walk on the beach. My heart skips a beat. I like to massage your feet.
He wrote his partner's name in a post on New Year's Eve.
The court heard testimony from former Manchester United chief executive David Gill and other people.
The chairman of the League Two club which Mr Giggs co-owns described him as a gentleman.
She said that in meetings, she finds him attentive. I have always gotten along well with him.
He is a nice person. One of the quietest people I've met. It was very relaxing and laid back.
Mr Gill said that Ryan was a professional.
The coach and player took their jobs very seriously, according to Mr Gill.
He said that he is always very nice. He was honest. He can tell you what he said.
He was a nice person with a sense of humor.
Ryan is always willing to help and improve.