What does Ryu mean?
From Japanese 龍 / 竜 (ryuu) 'dragon'. Hedge: more often a dragon-bearing element within compound names than a standalone given name, and the same sound is written with other kanji meaning 'noble/prosperous' (隆), 'flow' (流) or 'lapis lazuli' (琉); the dragon meaning applies to the 龍/竜 spelling. Romanized Ryu or Ryuu (the macron/double-u marks a long vowel).
What does Tatsuo mean?
Japanese given name read as 'dragon man' when written with a dragon element plus 'o/man', e.g. 竜雄 / 龍男 (竜/龍 'dragon' + o 'man/hero'). Hedge: strongly kanji-dependent; some spellings use 達 'attain' or other elements with no dragon sense, so only the 竜/龍/辰 writings genuinely mean dragon.