Acanthus the Lacedaemonian, was victor in two footrace events, the diaulos

Diaulos (running race)

Diaulos was a double-stadion race introduced in the 14th Olympiad of the ancient Olympics...

  and dolichos

Dolichos (running race)

Dolichos or Dolichus in ancient Olympics was a long-race introduced in 720 BC. Separate accounts of the race present conflicting evidence as to the actual length of the dolichos. However, the average stated length of the race was approximately 18-24 laps, or about three miles...

 , in the Olympic games of 720 BC. He was also, according to some accounts, the first who ran naked in these games. Other accounts ascribe this to Orsippus

Orsippus

Orsippus was an ancient Greek runner from Megara who was famed as the first to run the footrace naked at the Olympic Games and "first of all Greeks to be crowned victor naked." Others argue that it was Acanthus instead who first introduced Greek athletic nudity. Orsippus won the stadion-race of the...

 the Megarian. Thucydides

Thucydides

Thucydides was a Greek historian and author from Alimos. His History of the Peloponnesian War recounts the 5th century BC war between Sparta and Athens to the year 411 BC...

 says that the Lacedaemonians were indeed the first who contended naked in gymnastic games, although he does not mention Acanthus by name.