Father of Microsoft co-founder Bill Gates died on Monday, his son has confirmed. William H. Gates II, also known as Bill Gates Sr was 94 and “his health had been declining”, Bill Gates wrote in his official blog.

Gates Sr was an Army veteran and a founding partner in a Seattle law firm, according to his official biography.

Reflecting on his father’s influence on his life, Gates wrote that when he was a kid, his dad wasn’t prescriptive or domineering, but didn’t let him coast along at things he was good at. Instead, he pushed him for things he hated or thought he couldn’t do, like swimming and soccer.

His father also worked at the Bill & Melinda Gates Foundation, the Microsoft co-founder wrote. He said they worked together not as father and son, but as friends and colleagues. 

“When we started doing so in a big way at the foundation, we had no idea how much fun we would have. We only grew closer during more than two decades of working together,” he wrote.

Gates said his father had a profoundly positive influence on his most important roles, as husband and father.

His father wrote a letter to him on his 50th birthday. “It is one of my most prized possessions,” Gates wrote.

“In it, he encouraged me to stay curious,” he wrote.

“The experience of being your father has been… incredible,” Gates Sr wrote in the letter.

The billionaire philanthropist wrote that people would often ask his dad if he was the real Bill Gates. 

“The truth is, he was everything I try to be,” Gates wrote.