Philippine president Benigno Aquino was described by the former United States' envoy as "diffident and unassertive", secret cables published by anti-secrecy website Wikileaks reveal.
US ambassador to Manila Kristie Kenney filed the series of unflattering cables after then senator Aquino had declared his presidential candidacy and during the election campaign, the website said.
"Previous contacts with Senator Aquino, often accompanying his mother... left the impression of a diffident, unassertive man continuing a political tradition handed on by his parents but not carving his own legacy," said Kenney.
Wikileaks said the dispatch was made after the son of the late democracy icon and former president Corazon Aquino called on the US envoy at her home in January 2010.
"Senator Aquino's confident, energetic announcement today was a stark contrast his diffident performance last week," she wrote after Aquino announced his candidacy in September 2009.
"It remains unclear whether Aquino can turn his shy, reserved qualities into strengths," she said.
The cables suggested Kenney, who ended her Philippine posting last year, remained unimpressed to the end.
"Unlike other major presidential candidates... Aquino was vague on specific policies he would pursue if he won office," she said of the meeting at her home.
She conceded: "Aquino may be perceived as having had a lacklustre political career, but he also appears to have a relatively clean record with no baggage of scandals, which could be a distinct advantage."
Responding to the revelations presidential spokesman Ricky Carandang suggested Kenney had sided with the incumbent leader's predecessor Gloria Arroyo.
"We normally don't comment on purportedly leaked cables but it's quite consistent with talk that went on in the diplomatic community at the time that Ambassador Kenney had been co-opted by the Arroyo regime," he told AFP.