MONACO (AP) — As Usain Bolt races toward the end of a great career, Wayde van Niekerk is considered to be track and field's next big star.

"That's a massive, massive responsibility," Van Niekerk said on Thursday. He set a stunning 400-meter world record in 43.03 seconds while winning the Olympic title last year.

He spoke in Monaco ahead of Herculis meeting on Friday in the Diamond League series where he will be a main attraction with Bolt, who will run one of his last competitive 100 races.

"I find it extremely difficult to even come close to what Usain has represented in his charismatic way," Van Niekerk said.

The softly spoken South African has talked with Bolt "quite a few times" about revealing more of his character.

"Usain has set the bar quite high both with his personality and his performances," Van Niekerk said, adding that he is "slowly but surely" coming out of his shell. "It's tough for us to catch up when it comes to personality because he (Bolt) naturally has it.

"At the end of the day you really just need to be you. It is the performances that make me a great athlete."

There was greatness on the Rio de Janeiro track last August when Van Niekerk eclipsed Michael Johnson's world mark of 43.18 some thought was unbeatable.

Now a regular question is where and when the first sub-43 time will be run — possibly at the world championships in London in two weeks.

"I can definitely think of a 42," Van Niekerk acknowledged. "It's bound to happen. I just need to have the right race and the right conditions and the right perfect moment."

Van Niekerk seems in top shape. He ran a world-leading 43.62 this month at Lausanne, Switzerland, and eased up near the end of his only 400 so far in the European summer season.

He also took another Johnson mark when setting a world-best of 30.81 in the seldom-raced 300 last month in the Czech Republic. His best 200 time of 19.84, in Jamaica last month, is second in the world this year.

For good measure, Van Niekerk also has a 9.94 in the 100 that is faster than any Bolt competitive time this season.

"I doubt it is the end of where I can be," Van Niekerk said of his times in the shorter sprints.

Still, he has only respect for eight-time Olympic champion Bolt, whose farewell season will leave a big gap the sport will struggle to fill.

"We all thought, 'Is this really possible?'" Van Niekerk said of growing up watching the Jamaican great set world records and winning Olympic and world titles. "He has also inspired us so much."