Gyoshu and Kakuja are two scientists of the same race who work for Lord Slug and look exactly the same. They were the only minions of Slug who were not fighters.
When Gyoshu is asked by Lord Slug how long it will take to "fix" Earth, his answer (10 days) does not satisfy his leader and he is swiftly killed with a Ki Blast. His successor, Kakuja, manages to "fix" Earth in less than half the time that Gyoshu said (three days). Kakuja was unintentionally killed by Lord Slug when the Namekian accidentally blasted his own ship when he was trying to hurt Gohan.
Gyoshu seems to have more of a coward-like attitude, while Kakuja has a more serious and evil tone.