After making a slow start to the 2014-15 Premier League season, Lukaku has returned to the form that saw Martinez spend a club-record £28million to make the Belgium international's stay at Goodison Park permanent.
Lukaku scored the opening goal in Everton's 2-1 victory over West Ham United on Saturday.
The former Chelsea front man has now found the back of the net in three of his past five Premier League fixtures and Martinez believes the 21-year-old has the potential to be the best striker in the world.
"Remember that the assessment of Rom is what he brings to the side. Nobody else in our squad can give us what he gives us," said Martinez.
"He is someone that holds up the ball and brings a lot of fear to the opposition because they always get players around him which opens space at all times. He's got power, he's got pace, he's a clinical footballer driving the ball - I've been delighted with Rom.
"The reality as well is that after the World Cup it's been difficult for him to get his best physical level and we need to help him towards that but I've been delighted with what he's done, although I still know he has loads to do because his potential is immense.
"I think he's doing exactly what the team needs. He's such a winner that he wants to become the best striker in the world and he's got the potential to do that."
