Ivan Boesky was a Wall Street financier who became notorious for his involvement in insider trading during the 1980s. He was known for his aggressive takeover tactics and his use of arbitrage, which earned him the nickname 'The King of Wall Street'. He was also known for his association with Michael Milken, who was convicted of securities fraud in 1989. Boesky was indicted in 1986 and pleaded guilty to one count of conspiracy to commit securities fraud. He was sentenced to three years in prison and fined $100 million. His initials, IVAN, are a four-letter solution to the crossword clue. ARBS is another four-letter solution to the crossword clue, and it stands for 'arbitrageurs', which were people who took advantage of price discrepancies in different markets.